Is auto increment a constraint?

Is auto increment a constraint in SQL?

The second piece of the puzzle is the IDENTITY constraint, which informs SQL Server to auto increment the numeric value within the specified column anytime a new record is INSERTED .

What is auto increment?

Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table. Often this is the primary key field that we would like to be created automatically every time a new record is inserted.

Is auto increment only for primary key?

There can be only one AUTO_INCREMENT column per table, it must be indexed, and it cannot have a DEFAULT value. So you can indeed have an AUTO_INCREMENT column in a table that is not the primary key.

Does auto increment need not null?

You don't have to specify NOT NULL on the column definition with AUTO_INCREMENT . You can leave it off, and MySQL will make the column NOT NULL . And if you specify NULL in place of NOT NULL , MySQL will accept the syntax, but it will ignore that, and make the column NOT NULL anyway.