Question

I’m getting a syntax error on the following query:


SELECT 1,2 WHERE 1=1


But this query works fine:


SELECT 1,2 FROM (SELECT 1) t WHERE 1=1;


It almost looks like a WHERE clause always needs a table. Sometimes, in the depth of a complex query it’s nice to use a SELECT/WHERE combo to turn on and off certain features. Is there a way to not always add the FROM (SELECT 1) t?

Edit:

I found another similar issue

(SELECT 1 x)
UNION
(SELECT 2)
WHERE 1=1

gives a syntax error, but this does not:

SELECT x
FROM
(
    (SELECT 1 x)
    UNION
    (SELECT 2)
) t
WHERE 1=1

I’m using 5.1.48-community MySQL Community Server (GPL). Is anyone else seeing this?

Answer 1

This:

SELECT  1 x
UNION
SELECT  2
WHERE   1 = 1

is two queries, combined with UNION. The second query:

SELECT  2
WHERE   1 = 1

is invalid, since it misses a FROM clause while still using WHERE.

This:

SELECT  x
FROM    (
        SELECT 1 x
        UNION
        SELECT 2
        ) t
WHERE   1 = 1

is a SELECT from an inline view, which is again, two queries combined with a UNION.

Neither of the queries uses WHERE, so it’s OK for them not to have a FROM. Both queries are valid, and the resulting query is too.