MySQL ADD PRIMARY KEY clause

Overview

In this tutorial, we will learn about ADD PRIMARY KEY clause in MySQL. A primary key or just key is a column or set of columns in a table that can uniquely identify a row within the table. To add a primary key a table, we can use the ALTER TABLE with the clause, and the name of the columns.

Syntax

The general syntax for the statement is a follows:

ALTER TABLE <table_name> ADD PRIMARY KEY <index_name> (index_columns)

Example

Let’s look the primary key constraint to a sample demo table. The table structure is shown below:

mysql> ALTER TABLE keydemo ADD PRIMARY KEY pri_key (ID);

Query OK, 0 rows affected (0.22 sec)
Records: 0 Duplicates: 0 Warnings: 0

ADD PRIMARY KEY

Issue the DESCRIBE statement on the table.

mysql> DESC keydemo;

+——-+————-+——+—–+———+——-+
| Field | Type | Null | Key | Default | Extra |
+——-+————-+——+—–+———+——-+
| ID | int | NO | PRI | NULL | |
| FName | varchar(50) | NO | | | |
| LName | varchar(50) | NO | | | |
+——-+————-+——+—–+———+——-+
3 rows in set (0.03 sec)

ADD PRIMARY KEY Example