MySQL IF(SELECT) statement

Question

I've got a MySQL statement that's failing to compile, can anyone give me a basic example of how it should work? Semi pseudo-code:

IF (SELECT 'id' FROM terms WHERE name = 'thename' IS NULL) THEN
# Do this...
ELSE
# do this...
END IF

I just can't get any IF statement to work at all, not even a test one like:

IF(1=1) 
THEN SELECT "works"
END IF

Is this a SQL statement or a stored procedure? The form you're using here is only for stored procedures, as made clear in the documentation. — tadman
– tadman, Commented Sep 5, 2013 at 14:55
Depending on what your "Do this" bit is, you might be better off using the expression form of IF rather than the statement form. — Jeremy Smyth
– Jeremy Smyth, Commented Sep 5, 2013 at 14:59

Kermit · Accepted Answer · 2013-09-05 14:58:04Z

6

For your first example, you're not evaluating the condition. You need to move the IS NULL outside the SELECT:

IF (SELECT 'id' FROM terms WHERE name = 'thename') IS NULL THEN
...

If you're running this inside a SELECT statement, you may want to use CASE:

SELECT
    CASE
        WHEN (SELECT 'id' FROM terms WHERE name = 'thename') IS NULL THEN ...
    END

Otherwise, see the IF documentation.

answered Sep 5, 2013 at 14:58

Kermit

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