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Oracle SQL Tutorial 18 - How to Create Foreign Keys
 
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In this video we are going to be creating foreign keys. I highly recommend watching the previous video before you watch this one. Essentially, we are creating a very simple database for a system where we can create projects and add people to those projects. We started with the users table: --Delete the table if needed: --DROP TABLE users; CREATE TABLE users( user_id NUMBER, username VARCHAR2(50 CHAR) UNIQUE, CONSTRAINT users_pk PRIMARY KEY (user_id) ); Now we are going to create a table for projects with a column that is a foreign key to the username. We're going to want to make this match data types: CREATE TABLE projects( project_id NUMBER, project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) ) Next, we need to add the column attributes we decided on last video: CREATE TABLE projects( project_id NUMBER, project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) NOT NULL ) NOT NULL because we want every project to have a creator, but we are not labeling UNIQUE because that means we could only have a specific username once in the table. We want to allow a user to create multiple projects. We also need to add a primary key: CREATE TABLE projects( project_id NUMBER, project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) NOT NULL, CONSTRAINT projects_pk PRIMARY KEY (username) ) Now, the question that remains is, how can I tell Oracle that I want the username to reference the username column of the other table? We have to make a foreign key constraint. As you've learned from the previous videos, there are about three ways to create constraints. You can do it inline at the column level, unnamed. You can do it at the column level, named, and you can do it at the Table level, named. Usually the table-level is preferred, but I will quickly remind you how to do all three again. CREATE TABLE projects( project_id NUMBER, project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) NOT NULL REFERENCES users (username), CONSTRAINT projects_pk PRIMARY KEY (project_id) ) This works, but if we want to name it, we should do this: CREATE TABLE projects( project_id NUMBER, project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) NOT NULL CONSTRAINT projects_users_fk REFERENCES users (username), CONSTRAINT projects_pk PRIMARY KEY (project_id) ) This works, but the preferred method is to do it at the table level: CREATE TABLE projects( project_id NUMBER, project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) NOT NULL, CONSTRAINT projects_pk PRIMARY KEY (project_id), CONSTRAINT projects_users_fk FOREIGN KEY (creator) REFERENCES users (username) ) Great! So you've learned how to create a foreign key, now we can see it inside of Oracle SQL Developer. One important thing when it comes to foreign keys is what happens when have data in your database and you try to delete the parent row that a row in the child table references? In the next video we are going to configure that using ON DELETE. See you all then and if you enjoy this series, please do me a huge favor by liking the video and subscribing to my YouTube channel. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELP ME! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 26813 Caleb Curry
45. Primary Key and Foreign Key Constraints in PL/SQL Oracle
 
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In this video you will learn about Primary Key and Foreign Key Constraints in PL/SQL Oracle. For Support =========== Email: [email protected] Contact Form: http://www.learninhindi.com/home/contact Our Social Media ================ Facebook: https://www.facebook.com/LearnInHindi Twitter: https://twitter.com/LearnInHindi For Training & Videos ===================== For more videos and articles visit: http://www.learninhindi.com Free Java Programming In Hindi Course ===================================== https://www.youtube.com/playlist?list=PLOZ3jentlCDAwwhMyoLISrxkXTADGp7PH Free Oracle PL/SQL Programming In Hindi Course ============================================== https://www.youtube.com/playlist?list=PLB5DA82419C2D99B6 Free C Programming In Hindi Course ================================== https://www.youtube.com/playlist?list=PLOZ3jentlCDAxKpBLMWogxSdy6BZcsAJq Trips & Tricks Channel ====================== https://www.youtube.com/channel/UCGmLfkuCo-3lHHJXRJ9HUMw Programming in Hindi Channel ============================ https://www.youtube.com/channel/UCudElIDgwNrybeAvXIy1HZQ
Views: 12910 ITORIAN
SQL tutorials 18: SQL Foreign Key Constraint By Manish Sharma
 
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SQL Tutorial 18: SQL foreign key constraint. Topic covered in this tutorial 1. Defining SQL foreign key using create table at column level 2. Defining SQL foreign key using create table at table level 1. Defining SQL foreign key using Alter Table statement Links Website article: http://www.rebellionrider.com/sql-foreign-key.htm Primary key tutorial: http://www.rebellionrider.com/sql-foreign-key.htm Create Table Tutorial: http://www.rebellionrider.com/sql-create-table.html Tool used in this tutorial is SQL Developer. This tutorial series is part of SQL expert exam certification training. if you are preparing for SQL certification you can use my tutorials. This SQL Tutorial is a part of free training. Copy Cloud referral link || Use this link to join copy cloud and get 20GB of free storage https://copy.com?r=j7eYO7 Contacts E-Mail [email protected] Twitter https://twitter.com/rebellionrider Instagram http://instagram.com/rebellionrider Facebook. https://www.facebook.com/imthebhardwaj Linkedin. http://in.linkedin.com/in/mannbhardwaj/ Thanks for linking, commenting, sharing and watching more of our videos This is Manish from RebellionRider.com Foreign key is an Input/output data constraint which is also known as referential integrity constraint. Foreign key represent a link or say a relationship between columns of tables. Similar to primary key constraint Foreign Key constraint is also of two types. Simple Foreign key constraint and Composite Foreign key constraint. Constraint which involves only one column in foreign key in child table and one column in reference key in parent table is called Simple Foreign Key. While the constraint which involves more than one column in foreign key in child table and more than one column in reference key in the parent table is called Composite Foreign Key.
Views: 105800 Manish Sharma
SQL tutorials 17: SQL Primary Key constraint,  Drop primary Key
 
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Blog link: http://www.rebellionrider.com/sql-primary-key.htm SQL tutorial on Primary key / SQL Primary key, In this tutorial you will learn about simple primary key, composute primary key, how to drop primary key. defining primary key using create table and alter table along with many other things. Tool used in this tutorial is SQL Developer. This tutorial series is part of SQL expert exam certification training. if you are preparing for SQL certification you can use my tutorials. This SQL Tutorial is a part of free training. Copy Cloud referral link || Use this link to join copy cloud and get 20GB of free storage https://copy.com?r=j7eYO7 Contacts E-Mail [email protected] Twitter https://twitter.com/rebellionrider Instagram http://instagram.com/rebellionrider Facebook. https://www.facebook.com/imthebhardwaj Linkedin. http://in.linkedin.com/in/mannbhardwaj/ Thanks for linking, commenting, sharing and watching more of our videos This is Manish from RebellionRider.com So Primary Key There are two types of Primary keys First is Simple primary Key: Primary key which Involves only one column and Second is Composite Primary Key: Primary Key which involves more than one column. We will start with Simple primary key. You can create Primary key either with Create Table statement of by using Alter table Statement. Let's define simple primary key using create table statements. With create table statement we can either define primary key at column level or at table level. We will start with defining Primary key at column level using create table statement. You just have to put keyword Primary key after data type and size of column while defining a column of a table. Here oracle server will create a primary key on product id with default constraint name which will be slightly difficult to understand. You can give your own name to your constraint which is also a good practice.
Views: 104226 Manish Sharma
SQL Server 27 - How to Create FOREIGN KEY Constraints
 
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In the previous video we set up an entire table. The problem with this table is that the species column is just plain text. The problem with this is that there is a higher probability of incorrect data and if we have tons of animals in here there will be a lot of redundant information. The solution to this is to change this species to a foreign key to another table. Remember that when you create a foreign key it is a child to a parent. The thing you need to know is that the parent has to exist before the child so the child has something to reference. So let's create the parent table. CREATE TABLE Species( ID INT PRIMARY KEY IDENTITY, Species VARCHAR(50) NOT NULL UNIQUE, FriendlyName VARCHAR(50) NOT NULL //NOT UNIQUE because multiple rows could be same category (Ex: Bunny) ); Now, the friendly name will likely have redundant data, so maybe later we can add a table for animal categories or something, but let's not overwhelm ourselves quite yet. Maybe in a few videos. Now that we have created that table, we can recreate the table that references it. The first thing to know when creating a foreign key is that the data type must match. Because the ID column in the species table is of type INT, we should make our Species column in the Animals table also of type INT. Secondly, to make this a foreign key we add REFERENCES Species(ID) to the Species column. DROP TABLE IF EXISTS Animals; CREATE TABLE Animals( ID INT PRIMARY KEY IDENTITY, Name VARCHAR(50) NOT NULL, Species INT NOT NULL REFERENCES Species(ID), ContactEmail VARCHAR(50) NOT NULL UNIQUE ); ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Support me! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 10510 Caleb Curry
How to get Parent Table, Reference Table, Foreign Key Constraint Name and Columns in SQL Server-P 71
 
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SQL Server / T-SQL Tutorial Scenario: You are working as SQL Server Developer, you are asked to provide the query that should return all the parent tables, reference tables, Foreign Key Constraints and Columns used in Foreign Key Constraint definition. Link to scripts used in SQL Server / TSQL Tutorial Video http://www.techbrothersit.com/2016/04/how-to-get-parent-table-reference-table.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 3577 TechBrothersIT
Oracle SQL Tuning with Foreign Key Constraints
 
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Learn how to tune SQL with Constraints! In this lesson (2 of 5), OCM John Watson demonstrates how to improve query performance by adding foreign key constraints. See all lessons, free at http://www.skillbuilders.com/oracle-database-sql-tuning-with-constraints.
Views: 447 SkillBuilders
Foreign Key | Database Management System
 
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To ask your doubts on this topic and much more, click on this Direct Link: http://www.techtud.com/video-lecture/lecture-foreign-key IMPORTANT LINKS: 1) Official Website: http://www.techtud.com/ 2) Virtual GATE: http://virtualgate.in/login/index.php Both of the above mentioned platforms are COMPLETELY FREE, so feel free to Explore, Learn, Practice & Share! Our Social Media Links: Facebook Page: https://www.facebook.com/techtuduniversity Facebook Group: https://www.facebook.com/groups/virtualgate Google+ Page: https://plus.google.com/+techtud/posts Last but not the least, SUBSCRIBE our YouTube channel to stay updated about the regularly uploaded new videos.
Views: 281638 Techtud
Oracle Tutorials | Primary key & Foreign Key Reference key Relationship in Oracle | by Mr.Sudhakar L
 
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Oracle Tutorials | Primary key & Foreign Key Reference key Relationship in Oracle | by Mr.Sudhakar L #Oracle #Tutorials #Videos ** For Online Training Registration: https://goo.gl/r6kJbB ► Call: +91-8179191999 #OracleTutorials | #Primary_key_ForeignKeyReference ► Visit Our Website for Classroom Training: https://nareshit.in ► For Online Training: https://nareshit.com/ -------------------------- ► About NareshIT: "Naresh IT is having 14+ years of experience in software training industry and the best Software Training Institute for online training, classroom training, weekend training, corporate training of Hadoop, Salesforce, AWS, DevOps, Spark, Data Science, Python, Tableau, RPA ,Java, C#.NET, ASP.NET, Oracle, Testing Tools, Silver light, Linq, SQL Server, Selenium, Android, iPhone, C Language, C++, PHP and Digital Marketing in USA,Hyderabad, Chennai and Vijayawada,Bangalore India which provides online training across all the locations -------------------------- ► Our Online Training Features: 1.Training with Real-Time Experts 2.Industry Specific Scenario’s 3.Flexible Timings 4.Soft Copy of Material 5. Share Videos of each and every session. -------------------------- Please write back to us at [email protected]/[email protected] or Call us at USA: +1404-232-9879 or India: +918179191999 ** Check The Below Links** ► For Course Reg: https://goo.gl/r6kJbB ► Subscribe to Our Channel: https://goo.gl/q9ozyG ► Circle us on G+: https://plus.google.com/NareshIT ► Like us on Facebook: https://www.facebook.com/NareshIT ► Follow us on Twitter: https://twitter.com/nareshitech ► Follow us on Linkedin: https://in.linkedin.com/company/naresh-i-technologies ► Follow us on Instagram: https://www.instagram.com/nareshitech/
Views: 1051 Naresh i Technologies
Oracle SQL Tutorial 6 - Relationships and Primary and Foreign Keys - Database Design Primer 3
 
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HAPPY VALENTINES DAY!!! Let's talk relationships.. This is the 6th video in your Oracle Database series. We are discussing database relationships which are a key feature of relational database management systems. We first discussed entities and attributes. I talked about how each entity is assigned a table and each attribute is a column within a table. We moved on to the three kinds of relationships. The first was one-to-one. This describes an entity and an attribute. A piece of data that is exclusive to an entity is, by definition, an attribute of that entity. This is stored in one table with the attribute being a column within this table. The second relationship is one-to-many. This relationship is between two entities. The way we properly store this in a database is using a foreign key in the child table. Remember, the child table is the entity on the many side of the one-to-many relationship. Every row within the child table will have a value for the foreign key that references a primary key in the parent table. This assumes that the foreign key field is not optional (NOT NULL). If the foreign key is optional, than a reference is not required but any reference must be valid. The third kind of relationship is a many-to-many relationship. In this situation, we need 3 tables. The many-to-many relationship is broken up into two one-to-many relationships. The intermediary table will associate each entity from one table with the appropriate entities in the other table. There is debate as to whether this table needs a primary key. This is because you can intact use the combination of two foreign keys as a primary key. This works because we will never have two duplicate rows within the intermediary table and the two foreign keys work as a compound key because of this. We finally discussed primary keys and foreign keys. Primary keys are used to keep each row inside of a table unique. If this key is a computer generated number it is known as a surrogate key, otherwise it is known as a natural key. Natural keys have real world meaning. For example, a social security number may work, or an email address (in some situations), etc. Whichever type of key you choose is solely up to you and/or the company you may be working for. HELP ME! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://Twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 49606 Caleb Curry
FOREIGN KEY CONSTAINT IN ORACLE SQL
 
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This is a free video tutorial explaining about foreign key constraint in Oracle SQL database, the video explains about how the foreign key works, how it can be implemented with easy to understand examples. We have also shown practical demonstration on creating the foreign key constraint, and then encountering the part not found, and child record exists kind of integrity constraint.
Views: 905 Kishan Mashru
Working with Primary & Foreign key Constraint in SQL Server | SQL Server Tutorial
 
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** For Online Training Registration: https://goo.gl/r6kJbB ? Call: +91-8179191999 💡 Visit Our Website for Classroom Training: https://nareshit.in/sql-server-training/ 💡For Online Training: https://nareshit.com/course/sql-server-online-training/ #sqlserver #server #programming #course #Tutorials #Training #Videos -------------------------- -------------------------- 💡 About NareshIT: "Naresh IT is having 14+ years of experience in software training industry and the best Software Training Institute for online training, classroom training, weekend training, corporate training of Hadoop, Salesforce, AWS, DevOps, Spark, Data Science, Python, Tableau, RPA , Java, C#.NET, ASP.NET, Oracle, Testing Tools, Silver light, Linq, SQL Server, Selenium, Android, iPhone, C Language, C++, PHP and Digital Marketing in USA, Hyderabad, Chennai and Vijayawada, Bangalore India which provides online training across all the locations -------------------------- 💡 Our Online Training Features: 🎈 Training with Real-Time Experts 🎈 Industry Specific Scenario’s 🎈 Flexible Timings 🎈 Soft Copy of Material 🎈 Share Videos of each and every session. -------------------------- 💡 Please write back to us at 📧 [email protected]/ 📧 [email protected] or Call us at the USA: ☎+1404-232-9879 or India: ☎ +918179191999 -------------------------- 💡 Check The Below Links ► For Course Reg: https://goo.gl/r6kJbB ► Subscribe to Our Channel: https://goo.gl/q9ozyG ► Circle us on G+: https://plus.google.com/+NareshIT ► Like us on Facebook: https://www.facebook.com/NareshIT ► Follow us on Twitter: https://twitter.com/nareshitek ► Follow us on Linkedin: https://goo.gl/CRBZ5F ► Follow us on Instagram: https://goo.gl/3UXYK3
Views: 75189 Naresh i Technologies
Tutorial#60 Foreign key constraint in Oracle SQL Database| How to Create FOREIGN KEY Constraints
 
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How to Add Foreign key Constraint in Oracle SQL Database, Foreign key in SQL, what is Constraints and Types of Constraints in an Oracle SQL Database | integrity Constraints in SQL all above-mentioned question will be get answered in this video A foreign key means that values in one table must also appear in another table, there are two tables in foreign key constraint, parent table, and child table, A foreign key can be defined in either a CREATE TABLE statement or an ALTER TABLE statement. Explaining constraints and types of constraints in Oracle or Constraints in Oracle SQL database or Constraints is nothing but a set of rules which is applied to the columns of any table in the database --------------------- Assignment: ---------------------- https://drive.google.com/open?id=1K0iUiL_FRvercFBvSLVYHVMIed0U2GOL In this series we cover the following topics: SQL basics, create table oracle, SQL functions, SQL queries, SQL server, SQL developer installation, Oracle database installation, SQL Statement, OCA, Data Types, Types of data types, SQL Logical Operator, SQL Function,Join- Inner Join, Outer join, right outer join, left outer join, full outer join, self-join, cross join, View, SubQuery, Set Operator. follow me on: Facebook Page: https://www.facebook.com/LrnWthr-319371861902642/?ref=bookmarks Contacts Email: [email protected] Instagram: https://www.instagram.com/equalconnect/ Twitter: https://twitter.com/LrnWthR
Views: 67 EqualConnect Coach
Truncate Table With Foreign Key
 
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Truncate Table A Table With Foreign Key In SQL Server.
Views: 819 Pramadha just fun
Cannot truncate table because it is being referenced by a FOREIGN KEY constraint - SQL Tutorial P70
 
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SQL Server / TSQL Tutorial Scenario: You need to truncate a table but when you try to execute truncate table tableName. You get below error. Msg 4712, Level 16, State 1, Line 43 Cannot truncate table 'SchemaName.TableName' because it is being referenced by a FOREIGN KEY constraint. How would you truncate this table? Link to scripts used in SQL Server / TSQL Tutorial Video http://www.techbrothersit.com/2016/04/cannot-truncate-table-because-it-is.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 3447 TechBrothersIT
Oracle SQL Tutorial 17 - Designing Our Foreign Keys
 
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We are going to continue working with the users table that we've started with, but we are going to add a few tables. Imagine a system where you can create projects. And users can be added to these projects. So this could be some kind of productivity app or a project management solution, think of JIRA. We are going to start with three tables. The first table is going to be a users table that contains all of the information about each user's account. We are then going to have a table that is called projects. Each project will have data about the project and a foreign key that is the creator of the project. This is a situation where the database design depends a lot on the business rules and requirements of the application. Is it appropriate to have only one creator, or can it have multiple creators? We are going to design it with only one creator per project to increase simplicity. The third table is going to be used to record what users are part of certain projects. This situation is a many to many relationship because we've decided that one user can be a part of multiple projects and an individual project can have multiple members working on it. Because this is a many to many relationship, it calls for an intermediary table, project_users. First, we will draw out the user table. We will have a user_id, username, first_name, and last_name. Now, this is our parent table, because it has no foreign keys. Now, this is our parent table, because it has no foreign keys. Other tables are going to be referencing this table, so they would be the children. The project table will have a project_id, title, description, and creator. The column that needs to be a foreign key is the creator. Let's move on to the next table and we'll get back to the foreign key of the project table. The other table was project_users. Knowing that this is an intermediary table, immediately we know that the first two columns are going to be foreign keys to the each of the other tables. Now, let's ask the important questions about the foreign keys. Let's first start with the project table's user column. The first thing we need to ask is what column does it need to reference? Remember, the only options are the columns that are UNIQUE. Our candidates are user_id and username. For now, let's go with username as it makes things easier to work with. Once we go into learning about joins, we will talk about joining things by ID. Different people do it different ways, with the majority using only ID columns for primary and foreign keys, but it's important to be familiar with different ways of doing things. The important thing to remember is that keys should never change, so if we should only reference the username if a user's username will never change. Should the foreign key be labeled UNIQUE? If yes, it means that a user can only create one project. I vote no. Should the foreign key be labeled NOT NULL? If not, it means that a project can exist without a creator. I vote no. Moving on to the next table, I think I'll have the columns reference the project's id and user's id, so we can get some experience referencing surrogate keys. We can apply to these foreign keys the same questions we asked about the other foreign key, and I would encourage you to do so and really think about why. But I can tell you that we are not going to want them to be NOT NULL, but not UNIQUE. Now that we have a pretty decent database design, we can proceed with creating our database. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELP ME! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 11697 Caleb Curry
Create, Alter, Drop foreign Key constraint in SQL Server - Part 14
 
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Subscribe to IT PORT : https://www.youtube.com/c/itport28 SQL Server Tutorial in Tamil : https://www.youtube.com/playlist?list=PLouAaeZ4xQ64enJDwWVvN3KduuZRlUrb3 SQL Server Concepts in Tamil : https://www.youtube.com/playlist?list=PLouAaeZ4xQ67kdNIByJKAGBIBhor_h4Hs SQL Server Analytic Functions in Tamil : https://www.youtube.com/playlist?list=PLouAaeZ4xQ65XIU5azEUgLVrBKEl-jWMV SQL Server Tutorial : https://www.youtube.com/playlist?list=PLouAaeZ4xQ66AYrzPtxt2SeeR4UABcBcO SQL Server Concepts : https://www.youtube.com/playlist?list=PLouAaeZ4xQ66zRe8-nDDy-YHY2o0rmbn4 SQL Server Analytic Functions : https://www.youtube.com/playlist?list=PLouAaeZ4xQ64hTsEdhLsVBquE1vERWngX A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables. You can create a foreign key by defining a FOREIGN KEY constraint when you create or modify a table. In a foreign key reference, a link is created between two tables when the column or columns that hold the primary key value for one table are referenced by the column or columns in another table. This column becomes a foreign key in the second table. A table can have 253 foreign key constraints.
Views: 288 IT Port
Oracle SQL Tutorial 15 - How to Add Primary Key Constraints
 
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The goal of this video is to take the CREATE TABLE statement we have and walk through the different ways to create primary keys. This and foreign keys are the most common constraints, so we need to make sure that you have this one down. Once we have a more complex database design with multiple tables, we will learn the proper way to create foreign keys. For now, I am going to keep all of our constraints at the column level, unnamed. The only exception is the primary key, because that is what we are focusing on in this video. The first way to create the primary key is at the column level, unnamed. The primary key is very important because it what we use to distinguish rows from one another. Every table you create is going to need a primary key, and I suggest putting a lot of effort into making sure your keys are set up correctly and organized. --Delete the table if needed: DROP TABLE users; CREATE TABLE users( user_id NUMBER PRIMARY KEY, username VARCHAR2(50 CHAR) NOT NULL UNIQUE ) The next way is at the column level, but named: --Delete the table: DROP TABLE users; CREATE TABLE users( user_id NUMBER CONSTRAINT users_pk PRIMARY KEY, username VARCHAR2(50 CHAR)NOT NULL UNIQUE ) The general naming convention here is the table name followed by an underscore, followed by pk for primary key. Finally, the third way, which is at the table level, is the way we are going to create our primary key: --Delete the table: DROP TABLE users; CREATE TABLE users( user_id NUMBER, username VARCHAR2(50 CHAR) NOT NULL UNIQUE, CONSTRAINT users_pk PRIMARY KEY (user_id) ) Now, once you've created these constraints, you can use Oracle SQL Developer to find these constraints. Open your databases in the connections tab and find the table in the Tables folder. Double click your table and travel to the Constraints tab. You can tell here that the UNIQUE constraint still exists in this table, but it has a pretty disgusting name. It kind of wants to make me puke. Referencing that constraint in the future with that wacky name would be a burden. Engrave these three options in your head so that you can use any of them whenever you need and can read other peoples' code. Thank you for sticking with the series thus far. In the next video, we will be…doing something. See you then! :) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Support me on Patreon! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 17640 Caleb Curry
Candidate Key in DBMS (Candidate key, Primary Key, Foreign Key, Alternate Key, Super Key)
 
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Candidate key definition and understanding with the help of examples. Happy Learning and Keep rising.
Views: 89858 Edu Therapy
How to add Foreign key Constraint to existing table in SQL Server-SQL Server/TSQL Tutorial Part 68
 
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SQL Server / TSQL Tutorial Scenario: You have already created two tables dbo.Customer and dbo.Orders. Primary Key is created on CustomerId column in dbo.Customer table. Link to scripts used in SQL Server / TSQL Tutorial Video http://www.techbrothersit.com/2016/04/how-to-add-foreign-key-constraint-to.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 6644 TechBrothersIT
Part 12   Can we join two tables without primary foreign key relation
 
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Link for all dot net and sql server video tutorial playlists http://www.youtube.com/user/kudvenkat/playlists Link for slides, code samples and text version of the video http://csharp-video-tutorials.blogspot.com/2014/09/part-12-can-we-join-two-tables-without.html Can we join two tables without primary foreign key relation Yes, we can join two tables without primary foreign key relation as long as the column values involved in the join can be converted to one type. ID column in Departments table is not the primary Key and DepartmentId column in Employees table is not the foreign key. But we can still join these tables using ID column from Departments table and DepartmentId column from Employees table, as both the columns involved in the join have same data type i.e int. Select Employees.Name as EmployeeName, Departments.Name as DepartmentName from Employees join Departments on Departments.ID = Employees.DepartmentId The obious next question is, if primary foreign key relation is not mandatory for 2 tables to be joined then what is the use of these keys? Primary key enforces uniqueness of values over one or more columns. Since ID is not a primary key in Departments table, 2 or more departments may end up having same ID value, which makes it impossible to distinguish between them based on the ID column value. Foreign key enforces referential integrity. Without foreign key constraint on DepartmentId column in Employees table, it is possible to insert a row into Employees table with a value for DepartmentId column that does not exist in Departments table. The following insert statement, successfully inserts a new Employee into Employees table whose DepartmentId is 100. But we don't have a department with ID = 100 in Departments table. This means this employee row is an orphan row, and the referential integrity is lost as result Insert into Employees values (8, 'Mary', 'Female', 80000, 100) If we have had a foreign key constraint on DepartmentId column in Employees table, the following insert statement would have failed with the following error. Msg 547, Level 16, State 0, Line 1 The INSERT statement conflicted with the FOREIGN KEY constraint. The conflict occurred in database "Sample", table "dbo.Departments", column 'ID'.
Views: 125945 kudvenkat
Oracle SQL Tutorial 20 - How to Create Composite Primary Keys
 
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This video is going to be a tutorial on how to create composite and compound keys. The difference between a composite and compound key is that a composite key can consist of any columns while a compound key has to consist of columns that are all keys themselves. We will be working with a compound key because we are going to be using the an intermediary table that has two foreign keys. The combination of both of the keys have to be unique. First, if we have any other CREATE TABLE commands, we are going to comment those out. We will space out the CREATE TABLE to have each column on a line, then we will add constraints as needed. CREATE TABLE project_users( project_id, user_id ) Now, let's add the data types: CREATE TABLE project_users( project_id NUMBER, user_id NUMBER } Now, what about some column attributes? I'm going to make both of the columns NOT NULL because we always want the rows to have a user and a project: CREATE TABLE project_users( project_id NUMBER NOT NULL, user_id NUMBER NOT NULL } Now, let's add the foreign key constraints. Now, what do we name these? We are going to add a primary key that covers both of these columns, so I'm going to be a sinner and not give these constraints names: CREATE TABLE project_users( project_id NUMBER NOT NULL REFERENCES projects (project_id), user_id NUMBER NOT NULL REFFERENCES users (user_id) ) Now, the way we have it now is that if we delete a project in the project table, and there are any rows in the project_users table, it will throw an error and prevent deletion. I would prefer for it to also delete any project members. That would make sense because if you delete a project we want it to delete the associate between that project and certain users. The same goes for if we delete a user, we want their association with a certain project to be deleted. To do this, we need to add the ON DELETE command: CREATE TABLE project_users( project_id NUMBER NOT NULL REFERENCES projects (project_id) ON DELETE CASCADE, user_id NUMBER NOT NULL REFERENCES users (user_id) ON DELETE CASCADE, ) Finally, let's learn how to create a compound or composite key. literally, the only difference is that you put a comma and add the second table inside of the parenthesis. CREATE TABLE project_users( project_id NUMBER NOT NULL REFERENCES projects (project_id) ON DELETE CASCADE, user_id NUMBER NOT NULL REFERENCES users (user_id) ON DELETE CASCADE, CONSTRAINT project_users_pk PRIMARY KEY (project_id, user_id) ) Now, the combination of project_id and user_id cannot be null, is always unique, and has an index. The only thing we should do now is add a few indexes. We aren't done yet...In the next video we are going to figure out what columns would benefit from indexes and we'll add them to it. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELP ME! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 12970 Caleb Curry
SelectTec | Aula Nº 30 | Alter table add Foreign Key - Oracle SQL Developer
 
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syntax: ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (column1, column2, ... column_n) REFERENCES parent_table (column1, column2, ... column_n);
Views: 2124 SelectTec
Creating Primary and Foreign Keys in SQL Server 2012
 
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Dr. Soper shows how to create simple and composite primary keys and foreign key relationships in a SQL Server database using SQL Server Management Studio. Several different methods of creating keys and establishing relationships between tables are demonstrated.
Views: 438996 Dr. Daniel Soper
106. Create Table with Foreign Key in SQL Practical (Hindi)
 
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Oracle SQL Tutorial 19 - ON DELETE (SET NULL and CASCADE)
 
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Welcome everyone! Something you need to consider when you are creating foreign keys is what happens if you delete the parent? As a reminder, the parent is the row that has the value you are referencing in the row that has a foreign key. Why is this something important to consider? It's important because foreign keys need to protect us from two primary things, unacceptable INSERT statements, and unacceptable DELETE statements. Let's see what happens when we try to insert incorrect data into the table with the foreign key: INSERT INTO projects VALUES (1, 'Update website homepage', 'CalebCurry') The response tells us plainly that there is no such user in the users table. So this works correctly. Deleting data on the other hand works a bit differently because the database does not know what you want to do with the child row when you delete the parent from the parent table. By default, we will get an error message that prevents the parent from being deleted, but there are some other options. How do we configure this? This is where the ON DELETE statement comes in. We add the keywords ON DELETE right after the foreign key and then we can give it the option of CASCADE or SET NULL. CASCADE means that if we delete the parent, we are also going to delete the child. In our situation what that means is that if somebody creates a project in our project table and then that persons account gets deleted, all of the projects he owns will also be deleted. CASCADE: CREATE TABLE projects( project_id NUMBER, Project_name VARCHAR2(50 CHAR) UNIQUE, creator VARCHAR2(50 CHAR) NOT NULL, CONSTRAINT projects_pk PRIMARY KEY (project_id), CONSTRAINT projects_users_fk FOREIGN KEY (creator) REFERENCES users (username) ON DELETE CASCADE ) SET NULL will take the value in the child table and get rid of it. What you are left with is NULL. This means that we have an orphaned child. The first thought you might have is that it is a bad thing to have an orphaned child, but in databases that is not always so. In our application if we had it set to SET NULL, when a user account gets deleted the projects would remain in existence they would just lack a creator. This might be a good thing if you are concerned about the long term survival of a project, this might be the route you want to go. It ultimately depends on the application purpose. If you don't like CASCADE or SET NULL, you can leave the entire ON DELETE statement and just have Oracle throw an error when a parent is deleted. As for us, we are going to use ON DELETE CASCADE. We need to use this with extreme caution. If you are not careful, someday you will run a delete a row and that will cascade through you database deleting a bunch of stuff you didn't want to delete. Stuff happens, so make sure you back up your database every once in eternity. Now, in the last video we started with a database design that had three tables. We've only created two in this video. In the next video we are going to create the next one, which is a little special. Then we'll finish things up by adding some indexes. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Support me on Patreon! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 19107 Caleb Curry
Create, Alter, Drop foreign Key constraint in SQL Server - Part 14 Tamil
 
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Subscribe to IT PORT : https://www.youtube.com/c/itport28 SQL Server Tutorial in Tamil : https://www.youtube.com/playlist?list=PLouAaeZ4xQ64enJDwWVvN3KduuZRlUrb3 SQL Server Concepts in Tamil : https://www.youtube.com/playlist?list=PLouAaeZ4xQ67kdNIByJKAGBIBhor_h4Hs SQL Server Analytic Functions in Tamil : https://www.youtube.com/playlist?list=PLouAaeZ4xQ65XIU5azEUgLVrBKEl-jWMV SQL Server Tutorial : https://www.youtube.com/playlist?list=PLouAaeZ4xQ66AYrzPtxt2SeeR4UABcBcO SQL Server Concepts : https://www.youtube.com/playlist?list=PLouAaeZ4xQ66zRe8-nDDy-YHY2o0rmbn4 SQL Server Analytic Functions : https://www.youtube.com/playlist?list=PLouAaeZ4xQ64hTsEdhLsVBquE1vERWngX A foreign key (FK) is a column or combination of columns that is used to establish and enforce a link between the data in two tables. You can create a foreign key by defining a FOREIGN KEY constraint when you create or modify a table. In a foreign key reference, a link is created between two tables when the column or columns that hold the primary key value for one table are referenced by the column or columns in another table. This column becomes a foreign key in the second table. A table can have 253 foreign key constraints. Explained in Tamil
Views: 1156 IT Port
Oracle Primary Key Constraint 1 تعليم اوراكل
 
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by Mohamed El Desouki - محمد الدسوقى [email protected] Tel :00966 553450836 جامعة سلمان بن عبد العزيز - السعودية - الخرج How To Add Primary Key Constraint To a Table.إضافة قيد المفتاح الرئيسى للجدول Text Book: Fundamentals of Database Systems, 5th Edition, by Elmasri/Navathe, published by Addison-W oracle create table statement oracle drop table statement oracle constraints database constraints primary key constraint foreign key constraint check constraint null not null constraint unique constraint
add primary key and foreign key to join two table in oracle database
 
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add primary key and foreign key to join two table in oracle database
How to Drop Foreign Key Constraint in SQL Server Database - SQL Server / TSQL Tutorial Part 75
 
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SQL Server / T-SQL Tutorial Scenario: You are working as SQL Server developer and you need to prepare the script to drop the Foreign Key Constraint which was created on dbo.Orders table. Link to scripts used in SQL Server / TSQL Tutorial Video http://www.techbrothersit.com/2016/04/how-to-drop-foreign-key-constraint-in.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 4499 TechBrothersIT
108. Drop Foreign Key from Table in SQL (Hindi)
 
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Please Subscribe Channel Like, Share and Comment Visit : www.geekyshows.com
Views: 8576 Geeky Shows
Primary key and Foreign Key in DBMS
 
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Primary key vs Foreign key in DBMS. Key concepts in DBMS. (Candidate key, Primary Key, Foreign Key, Alternate Key, Super Key)
Views: 190523 Edu Therapy
Oracle Drop, Disable and Enable Constraints تعليم اوراكل
 
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by Mohamed El Desouki - محمد الدسوقى [email protected] Tel :00966 553450836 جامعة سلمان بن عبد العزيز - السعودية - الخرج How to Drop , Disable and Enable Constraints. كيف حذف و تعطيل و إعادة تشغيل القيود Text Book: Fundamentals of Database Systems, 5th Edition, by Elmasri/Navathe, published by Addison-W oracle create table statement oracle drop table statement oracle constraints database constraints primary key constraint foreign key constraint check constraint null not null constraint unique constraint
How To Insert Data Into Multiple Table Using Foreign Key
 
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Normally we create table and insert data into the table.But,Here we learn about how to insert data into multiple table. Normally,For inserting data into multiple table using foreign key but without using foreign key we can also insert data into multiple table.
Views: 91256 J&T Channel
Example on foreign key constraint and delete cascade
 
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Join discussion on http://www.techtud.com/video-illustration/following-table-has-two-attributes-and-c-where-primary-key-and-c-foreign-gate
Views: 9229 Techtud
Primary (PK) and Foreign Key (FK) Relation on Table without Cascade Rules Part 1 | MSSQL Training
 
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Views: 8875 Naresh i Technologies
Oracle SQL Tutorial 16 - Parent Child Relationships
 
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So far in this series we have discussed database design, creating tables, and constraints. We've brought up the concept of foreign keys, but we have not explained how to create them. That is the goal of this video and the upcoming videos. We want to study those foreign keys! Let's make them not so foreign. Let's learn the proper way to define a foreign key. As a reminder, a foreign key is a column that references a column of another table. The column it references must either be a primary key, or have the UNIQUE constraint. This means that every value inside of the column that is labeled as a foreign key, there must be that value in some row of the referenced column. As an example, imagine that we have the users table, and we have a table service_requests. We could have a column in the service_request that references a column in the users table. Usually this would be the primary key that is referenced, but there is nothing stopping you from referencing a unique column. Just for fun, let's go through an example using the username column. If we have a service_requests table, every single row within the table is going to be what some would consider an instance of a service_request. This means that the table columns are like the blueprint for what a service request looks like and then each row is an individual service request. If we have one of the columns labeled as a foreign key to the username of the users table, what does that mean practically? It means that for a single row, the value for that column must be a value that exists in the users table. We could have a service_request submitted by a user with the username of Yoloswagman. This means that there must be a row inside of the users table that has the value Yoloswagman for the username column. This brings up the concept of parent and child relationships. Yoloswagman in this situation is the parent, and his service request is the child. When we draw it out, it makes sense why a primary key must be UNIQUE. If we had two Yoloswagmans, the child would not know which column is the parent. The same applies if we were using IDs and we had So remember, always reference a primary key or a column with the UNIQUE constraint. Now, I have a question for you. Do foreign keys automatically have the UNIQUE constraint, just like primary keys? The answer is no. A parent row can have many child rows. It makes sense because the user could submit multiple service requests. Can we force the column to be unique? Absolutely. If that was the case, the user could only make one service request. Another question. Do foreign keys automatically have the NOT NULL constraint, just like primary keys? The answer is no. Essentially what this means is that a child could be created with no parent. Can we force the column to be NOT NULL? Absolutely. It is ok in some situations to allow the row to be null, but in this situation it makes no sense. It would be wise for us to add that constraint ourselves. So now that you understand some more differences between primary and foreign keys and parent child relationships, take all of these questions into consideration when you are creating foreign keys. In the next video, we are going to start a small project that is going to require multiple tables. We'll take a video to design our structure and then we'll get to creating those foreign keys in Oracle SQL Developer. Stick around and if you like these videos please be a serious supporter and subscribe to my channel. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELP ME! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 14846 Caleb Curry
How to disable all Foreign Key Constraint in SQL Server Database-SQL Server / TSQL Tutorial Part 77
 
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SQL Server / T-SQL Tutorial Scenario: You are working as SQL Server developer, You need to provide the scripts to disable all the Foreign Key Constraint in SQL Server database. This might be scenario where you need to load one time data and you are ok if data violate referential integrity. Link to scripts used in SQL Server / T-SQL Tutorial Video http://www.techbrothersit.com/2016/04/how-to-disable-all-foreign-key.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 1852 TechBrothersIT
How to Create Tables, Insert, Primary and Foreign Keys and Computed Column in SQL Server - Part 2
 
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My blog: How to Create tables http://biandsqldb.blogspot.ca/2016/04/how-to-create-tables-datatypes-primary.html Data types: https://msdn.microsoft.com/en-CA/library/ms187752.aspx
Views: 4185 TJ Kash
Primary key and Foreign key on Oracle In Telugu | Oracle in Telugu
 
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#KOTHA_ABHISHEK http://htmlintelugu1.blogspot.com http://cssintelugu1.blogspot.com http://javascriptintelugu1.blogspot.com http://sqlintelugu1.blogspot.com http://javaintelugu1.blogspot.com
Views: 6372 KOTHA ABHISHEK
How to Create Table with Foreign Key Constraint in SQL Server - SQL Server / TSQL Tutorial Part 66
 
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SQL Server / TSQL Tutorial Scenario: What is Foreign Key in SQL Server Table: Foreign Key in a table is a column or group of columns that provides a link between data in two tables. The Foreign Key in a table points to the primary key in another table. In this video you will learn how to create foreign key constraint. Link to scripts used in SQL Server / TSQL Tutorial Video http://www.techbrothersit.com/2016/04/how-to-create-table-with-foreign-key.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 2487 TechBrothersIT
61. ALTER TABLE for Adding Constraint in Column SQL (Hindi)
 
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Please Subscribe Channel Like, Share and Comment Visit : www.geekyshows.com
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Primary Key, Foreign Key, NOT NULL, DEFAULT, UNIQUE, and CHECK   ||  Table Constraints in SQL
 
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primary key Learn SQL - SQL CONSTRAINTS CONSTRAINTS - PRIMARY KEY, NOT NULL, etc - SQL Server constraints in dbms | constraints in sql in hindi Oracle SQL Tutorial - How to Add Column Constraints (Attributes) Oracle SQL Constraints Not Null, Primary Key, Unique, Foreign Key and Check Primary Key (PK) Constraint in SQL Server Unique key constraint SQL constraints Working with Primary & Foreign key Constraint in SQL Server | MSSQL Training NOT NULL, DEFAULT, CHECK Constraints (Domain Integrity) in SQL Server Introduction to SQL Constraints
SQL script to insert into many to many table
 
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Text Article http://csharp-video-tutorials.blogspot.com/2017/02/sql-script-to-insert-into-many-to-many.html Slides http://csharp-video-tutorials.blogspot.com/2017/02/sql-script-to-insert-into-many-to-many_6.html SQL Server Interview Questions and Answers text articles & slides http://csharp-video-tutorials.blogspot.com/2014/05/sql-server-interview-questions-and.html SQL Server Interview Questions and Answers playlist https://www.youtube.com/playlist?list=PL6n9fhu94yhXcztdLO7i6mdyaegC8CJwR All Dot Net and SQL Server Tutorials in English https://www.youtube.com/user/kudvenkat/playlists?view=1&sort=dd All Dot Net and SQL Server Tutorials in Arabic https://www.youtube.com/c/KudvenkatArabic/playlists In this video we will discuss how to insert data into a table that has many-to-many relationship Create table Students ( Id int primary key identity, StudentName nvarchar(50) ) Go Create table Courses ( Id int primary key identity, CourseName nvarchar(50) ) Go Create table StudentCourses ( StudentId int not null foreign key references Students(Id), CourseId int not null foreign key references Courses(Id) ) Go Students - Id column is identity column Courses - Id column is identity column StudentCourses - StudentId and CourseId columns are foreign keys referencing Id column in Students and Courses tables As you can see, StudentCourses is a bridge table that has many to many relationship with Students and Courses tables. This means a given student can be enrolled into many courses and a given course can have many students enrolled. Below is the question asked in an interview for SQL Server Developer role. Write a SQL script to insert data into StudentCourses table. Here are the rules that your script should follow. 1. There will be 2 inputs for the script Student Name - The name of the student who wants to enroll into a course Course Name - The name of the course the student wants to enroll into 2. If the student is already in the Students table, then use that existing Student Id. If the student is not already in the Students table, then a row for that student must be inserted into the Students table, and use that new student id. 3. Along the same lines, if the course is already in the Courses table, then use that existing Course Id. If the course is not already in the Courses table, then a row for that course must be inserted into the Courses table, and use that new course id. 4. There should be no duplicate student course enrollments, i.e a given student must not be enrolled in the same course twice. For example, Tom must not be enrolled in C# course twice. Answer : To avoid duplicate student course enrollments create a composite primary key on StudentId and CourseId columns in StudentCourses table. With this composite primary key in place, if someone tries to enroll the same student in the same course again we get violation of primary key constraint error. Alter table StudentCourses Add Constraint PK_StudentCourses Primary Key Clustered (CourseId, StudentId) Here is the SQL script that inserts data into the 3 tables as expected Declare @StudentName nvarchar(50) = 'Sam' Declare @CourseName nvarchar(50) = 'SQL Server' Declare @StudentId int Declare @CourseId int -- If the student already exists, use the existing student ID Select @StudentId = Id from Students where StudentName = @StudentName -- If the course already exists, use the existing course ID Select @CourseId = Id from Courses where CourseName = @CourseName -- If the student does not exist in the Students table If (@StudentId is null) Begin -- Insert the student Insert into Students values(@StudentName) -- Get the Id of the student Select @StudentId = SCOPE_IDENTITY() End -- If the course does not exist in the Courses table If (@CourseId is null) Begin -- Insert the course Insert into Courses values(@CourseName) -- Get the Id of the course Select @CourseId = SCOPE_IDENTITY() End -- Insert StudentId & CourseId in StudentCourses table Insert into StudentCourses values(@StudentId, @CourseId) If required, we can very easily convert this into a stored procedure as shown below. Create procedure spInsertIntoStudentCourses @StudentName nvarchar(50), @CourseName nvarchar(50) as Begin Declare @StudentId int Declare @CourseId int Select @StudentId = Id from Students where StudentName = @StudentName Select @CourseId = Id from Courses where CourseName = @CourseName If (@StudentId is null) Begin Insert into Students values(@StudentName) Select @StudentId = SCOPE_IDENTITY() End If (@CourseId is null) Begin Insert into Courses values(@CourseName) Select @CourseId = SCOPE_IDENTITY() End Insert into StudentCourses values(@StudentId, @CourseId) End Use the following statement to execute the stored procedure Execute spInsertIntoStudentCourses 'Tom','C#'
Views: 96834 kudvenkat
Could not drop object because it is referenced by a FOREIGN KEY constraint - SQL Server P74
 
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SQL Server / T-SQL Tutorial Scenario: You are working as SQL Server DBA or Developer, You need to drop a table from a database. When you execute drop table SchemaName.TableName statement, you get below error. Msg 3726, Level 16, State 1, Line 12 Could not drop object 'SchemaName.TableName' because it is referenced by a FOREIGN KEY constraint. Now we know that the table is referenced by Foreign Key Constraint. The problem is how to find which table has that Foreign Key Constraint that is referencing to this table. Link to scripts used in SQL Server / TSQL Tutorial Video http://www.techbrothersit.com/2016/04/could-not-drop-object-because-it-is.html Check out our website for Different SQL Server, MSBI tutorials and interview questions such as SQL Server Reporting Services(SSRS) Tutorial SQL Server Integration Services(SSIS) Tutorial SQL Server DBA Tutorial SQL Server / TSQL Tutorial ( Beginner to Advance) http://www.techbrothersit.com/
Views: 2838 TechBrothersIT
MySQL Tutorial for Beginners 17 - MySQL TRUNCATE TABLE with Examples
 
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In this post we will learn how to In this post we will learn How to Use MySQL TRUNCATE TABLE with Examples. Truncate Statement is used to delete all the rows of a table. MySQL TRUNCATE TABLE Syntax: TRUNCATE TABLE table_name ; The TRUNCATE action query removes all rows. we cannot truncate table with foreign key constraints But first let's see What is MySQL . MySQL is a very popular, open source database. Officially pronounced “my Ess Que Ell” (not my sequel). Handles very large databases; very fast performance. Why are we using MySQL? Free (much cheaper than Oracle!) Each student can install MySQL locally. Easy to use Shell for creating tables, querying tables, etc.Easy to use with Java JDBC. While installing MySQL, it will prompt you to create a root password . At this stage please select a safe and secure password . Make sure you remember the password, to use it later.MySQL tutorial for beginners and professionals with examples on CRUD, insert statement, select statement, update statement, delete statement, use database, keys, joins etc. MySQL Database is world's most popular open source database because of its consistent fast performance, high reliability and ease of use. MySQL has Open Source License i.e. it has free GNU General Public License. SQL (Structured Query Language) is the language used to insert and retrieve content. Clients make queries on the database to Retrieve, Insert, Update or Delete content. #MySQL #MySQLTutorial #ProgrammingKnowledge ----------------------Follow--------------------------------------------- My Website - http://www.codebind.com My Blog - https://goo.gl/Nd2pFn My Facebook Page - https://goo.gl/eLp2cQ Google+ - https://goo.gl/lvC5FX Twitter - https://twitter.com/ProgrammingKnow Pinterest - https://goo.gl/kCInUp Text Case Converter - https://goo.gl/pVpcwL ------------------Facebook Links ---------------------------------------- http://fb.me/ProgrammingKnowledgeLearning/ http://fb.me/AndroidTutorialsForBeginners http://fb.me/Programmingknowledge http://fb.me/CppProgrammingLanguage http://fb.me/JavaTutorialsAndCode http://fb.me/SQLiteTutorial http://fb.me/UbuntuLinuxTutorials http://fb.me/EasyOnlineConverter.
Oracle 12C Tutorial 20 - Constraints (Primary, Foreign, Unique, Null etc.)
 
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This Video Tutorial Will Describe about various constraints we can use with tables. Some of the constraints can used as table level or column level so also known as table level constraints and column level constraints. These command will also work on other versions of database like Oracle 11g Database, Oracle 10g Database, Oracle 9i Database, Oracle 8i Database, Oracle 8 Database and so on. In this video i explain Not Null Constraint, Unique key Constraint, Primary Key Constraint, Foreign Key - Reference key Constraint, Check constraint and user_constraints table. Full Syntax will be given in this video tutorial about how to use these constraints. Along with live example to execute Not Null Constraint, Unique key Constraint, Primary Key Constraint, Foreign Key - Reference key Constraint, Check constraint and user_constraints table . All the keywords, format, mandatory clauses etc are described in this video.
Oracle - SQL - Check Constraint
 
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Oracle - SQL - Check Constraint Watch more Videos at https://www.tutorialspoint.com/videotutorials/index.htm Lecture By: Mr. Anadi Sharma, Tutorials Point India Private Limited.
Oracle SQL Tutorial 14 - Column-Level and Table-Level Constraints
 
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In the previous video we talked about adding constraints at the column-level. We made it nice and simple by only requiring a few keywords, but the problem we were having is that we could not assign a name to the constraint, which many people like to do so we can reference easily if we need to at a later time. To do this, it requires a little bit more typing, but it will give us extra flexibility and many consider it to be the higher quality approach to adding constraints. Let's go though a simple example. Let's say we have a users table with a user_id column that we want to make a primary key. We will create the table like this: CREATE TABLE( user_ id NUMBER PRIMARY KEY ) Instead of adding the PRIMARY KEY keywords after the data type, we add: CONSTRAINT user_pk PRIMARY KEY Now, we have assigned the name user_pk to this constraint. You can do the same with other constraints, such as UNIQUE. The syntax would be CONSTRAINT username_un UNIQUE. The other way to create constraints requires to put all of our constraints at the bottom of our table creation rather than inline with the column. This type of constraint is known as a table-level constraints. To make a column a primary key using table-level constraints, we add it to the CREATE TABLE command as if it is another row and use the CONSTRAINT keyword to tell Oracle that what is coming is a constraint, not a column in our table. CREATE TABLE users( user_id NUMBER, username VARCHAR2(50 CHAR), CONSTRAINT username_un UNIQUE (username), CONSTRAINT users_pk PRIMARY KEY (user_id) ) The primary differences here is that you have to put the column you are talking about in parenthesis after the PRIMARY KEY keyword. That's because it's at the end of the table and you need a way to tell it what column you are talking about. The option of putting it at the end of the table has the added benefit in this situation because if we needed to have a primary key that is the combination of multiple columns, we can do that by just adding the other column in the PRIMARY KEY parenthesis right after a comma. In summary, there are three ways to make constraints. The first is at the column level, unnamed. The second is at the column level, named. The third is at the table level, also named. In the next video we are going to create a named constraint in Oracle SQL Developer, so stay tuned and be sure to subscribe! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Support me! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 17865 Caleb Curry
Oracle SQL Tutorial 11 - CREATE TABLE
 
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The way you create a table is to use the CREATE TABLE command. CREATE TABLE users() So in this situation, the name comes right after the TABLE keyword. The next thing we do is put all of the columns on a line that we want to put in our table. CREATE TABLE users( user_id, username, first_name, last_name ) Notice the naming conventions here. For this series we are going to make columns with what is known as snake casing. This is where each individual word is separated by an underscore. if you have more than one column, all of them have to have commas except the last one. The comma is a way to say that another column is coming, so you don't need to do it on the last one. Now you would think we were done, but we also have to say what data type each column is. Later we will extensively discuss data types so we can focus on them exclusively. For now, here are the data types we are going to use: CREATE TABLE users( user_id NUMBER, username VARCHAR2(50), first_name VARCHAR2(50), last_name VARCHAR2(50) ) Now, inside of the parenthesis for varchar2, we pass in a number... This is the max length of the string. But the question is, what is it measured in? The default is actually in bytes, not characters. For example if we have the string hello, it is 5 characters, but it might take up a total of 10 bytes of storage. So I would recommend adding the keyword char right after the number so it defaults to 50 characters, not bytes. CREATE TABLE users( user_id NUMBER, username VARCHAR(50 CHAR), first_name VARCHAR2(50 CHAR), last_name VARCHAR2(50 CHAR) ) This will work to create a table, but it's really missing a lot of information… which column is the primary key? Are we adding any indexes? Is there any thing else we need to say about these columns? So as you can tell, we are making progress, but there is still so much to learn. The biggest gotcha to remember from this video is that the data type VARCHAR ends in a 2, stupid, right? who would end the name of something with a 2? Once again, this is Caleb from CalebTheVideoMaker2, and we will catch you in the next one! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ HELP ME! http://www.patreon.com/calebcurry Subscribe to my newsletter: http://bit.ly/JoinCCNewsletter Donate!: http://bit.ly/DonateCTVM2. ~~~~~~~~~~~~~~~Additional Links~~~~~~~~~~~~~~~ More content: http://CalebCurry.com Facebook: http://www.facebook.com/CalebTheVideoMaker Google+: https://plus.google.com/+CalebTheVideoMaker2 Twitter: http://twitter.com/calebCurry Amazing Web Hosting - http://bit.ly/ccbluehost (The best web hosting for a cheap price!)
Views: 40594 Caleb Curry