mysql, isnull

The ISNULL function in MySQL is used to determine if an expression is NULL. It takes one or two arguments. If the first argument is NULL, it returns the second argument; otherwise, it returns the first argument. Here's an example:

SELECT ISNULL(NULL, 'Value is NULL');

This query will return 'Value is NULL' since the first argument is NULL. If the first argument was not NULL, the function would return the value of the first argument.

Note that MySQL also provides the IFNULL function, which is similar to ISNULL but only takes one argument. IFNULL returns the argument itself if it's not NULL; otherwise, it returns the second argument.

I hope this answers your question! Let me know if you need any further information.