如何使用默认约束为 mysql 中的列创建随机数？

Question

The DEFAULT constraint has no problem in accepting string or current date values. What i need is an constraint that will create an random 4 digit number every time an entity is created. I tried the following code but it returns an syntax error.

ALTER TABLE client_number ADD(code INT(4) DEFAULT FLOOR(RAND()*9999)+1111);

The above statement returns following error:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'floor(rand()*9999)+1111)' at line 1

Need solution.

Answer 1

This is too long for a comment.

The documentation is quite clear:

The DEFAULT value clause in a data type specification indicates a default value for a column. With one exception, the default value must be a constant; it cannot be a function or an expression.

The expression you have is not a constant, so it doesn't work. You would need to use a trigger instead.

Answer 2

Run the below query

ALTER TABLE table_name ADD field_name INT(4) NOT NULL DEFAULT (rand() * (9999 - 1000) + 1000) AFTER some_feild ;

The result gives a random number between 1000-9999