mysql - 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

Answer 1

对于您的第一个示例，您没有评估条件。您需要将IS NULL外部移动SELECT：

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

如果您在SELECT语句中运行它，您可能需要使用CASE：

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

否则，请参阅IF文档。