In this syntax, you separate columns in the column_list by commas (,). When the primary key has more than one column, you must use the PRIMARY KEY constraint as a table constraint. ) Code language: SQL (Structured Query Language) ( sql ) If the primary key has one column, you can use the PRIMARY KEY constraint as a column constraint: CREATE TABLE table_name( Typically, you define the primary key for a table in the CREATE TABLE statement. 1) Define a PRIMARY KEY constraint in CREATE TABLE The PRIMARY KEY constraint allows you to define a primary key of a table when you create or alter table. When you define a primary key for a table, MySQL automatically creates an index called PRIMARY. And you should ensure sure that value ranges of the integer type for the primary key are sufficient for storing all possible rows that the table may have.Ī primary key column often has the AUTO_INCREMENT attribute that automatically generates a sequential integer whenever you insert a new row into the table. This example we've created a primary key called contacts_pk that is made up of a combination of the last_name and first_name columns.Because MySQL works faster with integers, the data type of the primary key column should be the integer e.g., INT, BIGINT. We could also create a primary key with more than one field as in the example below: ALTER TABLE contacts In this example, we've created a primary key on the existing contacts table called contacts_pk. Let's look at an example of how to create a primary key using the ALTER TABLE statement in MySQL. column_n The columns that make up the primary key. constraint_name The name of the primary key. column_n) table_name The name of the table to modify. The syntax to create a primary key using the ALTER TABLE statement in MySQL is: ALTER TABLE table_name You can create a primary key in MySQL with the ALTER TABLE statement. So each combination of last_name and first_name must be unique in the contacts table.Ĭreate Primary Key - Using ALTER TABLE statement This example creates a primary key called contacts_pk that is made up of a combination of the last_name and first_name columns. We could also create a primary key with more than one field as in the example below: CREATE TABLE contactsĬONSTRAINT contacts_pk PRIMARY KEY (last_name, first_name)

It consists of only one column - the contact_id column. In this example, we've created a primary key on the contacts table called contacts_pk. ( contact_id INT(11) NOT NULL AUTO_INCREMENT,ĬONSTRAINT contacts_pk PRIMARY KEY (contact_id) Let's look at an example of how to create a primary key using the CREATE TABLE statement in MySQL.

See the MySQL CREATE TABLE statement for more detailed CREATE TABLE syntax as this is an over-simplification to demonstrate how to create a primary Key. column1, column2 The columns that you wish to create in the table. ) table_name The name of the table that you wish to create. The syntax to create a primary key using the CREATE TABLE statement in MySQL is: CREATE TABLE table_name You can create a primary key in MySQL with the CREATE TABLE statement. Create Primary Key - Using CREATE TABLE statement

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