myyis
asked on
union & order by
Hi there,
There are 2 SELECT statements joined by UNION.
The ORDER BY comes at the end.
The question is: Can I also put an ORDER BY after every SELECT? If I can, does that help the performance?
eg:
SELECT * FROM (SELECT * FROM TABLE1 ) ORDER BY ID DESC LIMIT 500 ) AS T1
UNION ALL
SELECT * FROM (SELECT * FROM TABLE2 ) ORDER BY ID DESC LIMIT 500 ) AS T2
ORDER BY DATETIME DESC
There are 2 SELECT statements joined by UNION.
The ORDER BY comes at the end.
The question is: Can I also put an ORDER BY after every SELECT? If I can, does that help the performance?
eg:
SELECT * FROM (SELECT * FROM TABLE1 ) ORDER BY ID DESC LIMIT 500 ) AS T1
UNION ALL
SELECT * FROM (SELECT * FROM TABLE2 ) ORDER BY ID DESC LIMIT 500 ) AS T2
ORDER BY DATETIME DESC
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