Example
In this example, we have created a table ‘Student123’ by defining column ‘RollNo’ with UNIQUE and NOT NULL constrAInts. Now, by describing the table we can see that ‘RollNo’ is the PRIMARY KEY column.
MySQL> Create table Student123(RollNo INT UNIQUE NOT NULL, Name varchar(20)); Query OK, 0 rows affected (0.25 sec) mysql> DESCRIBE Student123; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | RollNo | int(11) | NO | PRI | NULL | | | Name | varchar(20) | YES | | NULL | | +--------+-------------+------+-----+---------+-------+ 2 rows in set (0.04 sec)
以上就是如何在MySQL表中定义一个列为主键，而不使用PRIMARY KEY关键字。
