The ALTER TABLE statement below could be used to add a primary to the suppliers table: ALTER TABLE suppliers Let's pretend we've already set up a suppliers table in our database. column_n - The columns that make up the primary key.Įxample 1: Let's look at an example of utilising the ALTER TABLE statement in SQL to generate a primary key. constraint_name - The name of the primary key.This is the table to which a primary key should be added. table_name - The name of the table you want to change.The syntax to create a primary key using the ALTER TABLE statement in SQL is: ALTER TABLE table_name You can generate a primary key using the ALTER TABLE statement if your table already exists and you want to add one later. To drop or remove a SQL PRIMARY KEY constraint, use the following SQL statement: For MySQLįor Microsoft SQL SERVER / Microsoft ACCESS / ORACLE The primary key field(s) must already have been declared to not contain NULL values (when the table was first created). Note: If you want to add a primary key using SQL ALTER TABLE statement, To create a SQL PRIMARY KEY constraint on multiple fileds when the table is already created, use the following SQL statement: For Microsoft SQL Server / Oracle / Microsoft AccessĪDD CONSTRAINT chk_BookID PRIMARY KEY (BookID, BookName) To create a SQL PRIMARY KEY constraint on the "BookID" field when the table is already created, use the following SQL statement: For Microsoft SQL Server / Oracle / Microsoft Access / MySql SQL PRIMARY KEY Constraint on ALTER TABLE However, the VALUE of the primary key is made up of TWO FIELDS (BookID + BookName). Note: In the example above there is only ONE SQL PRIMARY KEY (chk_BookID). To allow naming of a SQL PRIMARY KEY constraint, and for defining a SQL PRIMARY KEY constraint on multiple fields, use the following SQL syntax: For Microsoft SQL Server / Oracle / Microsoft Access / MySqlĬONSTRAINT chk_BookID PRIMARY KEY (BookID, BookName) The above SQL statement will produce in an error, because '103' already exists in the BookID field, thus trying to insert another record with that value violates the SQL PRIMARY KEY constraint. VALUES (103, 'Sql Quick Programming', 'It descripe complete sql programming in short time') INSERT INTO Books (BookID, BookName, Description) Now executing the following below SQL statement: How to write and execute SQL programming using pl sql. It descripes how to write and execute SQL statement into database. Let's assume, if the "Books" table already contains the following records: Here, BookID field has a SQL PRIMARY KEY constraint to validate newly entered records for unique value. In the above example, the following SQL statement creates a new table called Books and adds four fields. The following SQL statement creates a SQL PRIMARY KEY constraint on the "BookID" field when the "Books" table is created: For MySqlįor Microsoft SQL Server / Oracle / Microsoft Access SQL PRIMARY KEY Constraint on CREATE TABLE Sql primary key constraint using primary key vs unique key, alter table add primary key, create table primary key, update and drop primary key,Ĭomposite primary key, unique key, create table sql server primary key, add constraint primary key Auto Generate, Auto Increment, Primary Key Name Convention,ĭifference between primary key, foreign key and unique key.
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