Simple SQL query too long - sql

Question

I just have a simple query. On SQL Server 2008, sometimes it queries too long, nearly hang, sometimes not. The same sql on Oracle server, it always return at once.
SELECT D.DESCITEM, D.LONGDESC, D.DESCTABL, D.DESCCOY, D.DESCPFX
FROM VM1DTA.DESCPF D, VM1DTA.ITEMPF I
WHERE D.DESCPFX='IT'AND D.DESCITEM=I.ITEMITEM AND I.VALIDFLAG='1'
AND D.DESCTABL = I.ITEMTABL AND D.DESCCOY = I.ITEMCOY AND "LANGUAGE" = 'E'
AND "VALIDFLAG" = '1' AND DESCTABL IN('T1680')
ORDER BY LONGDESC ASC;
Each table has about 100k records.
Could someone point me about the root cause? Thanks

Answer 1

I'm not sure what the issue is but your query could use some refactoring. This line looks unneeded as well "VALIDFLAG" = '1' because it has no prefix. The IN may have something to do with it.
SELECT D.DESCITEM, D.LONGDESC, D.DESCTABL, D.DESCCOY, D.DESCPFX
FROM
VM1DTA.DESCPF D INNER JOIN VM1DTA.ITEMPF I ON
D.DESCITEM=I.ITEMITEM
AND
D.DESCTABL = I.ITEMTABL
AND
D.DESCCOY = I.ITEMCOY
WHERE
D.DESCPFX='IT'
AND
"LANGUAGE" = 'E'
AND
I.VALIDFLAG='1'
AND
"VALIDFLAG" = '1'
AND
I.DESCTABL = 'T1680'
ORDER BY
LONGDESC ASC;
The other thing to look at is putting indexes on all of the join columns.
Hope this helps.

Answer 2

I find that joining two tables by free text fields takes up a lot of resource and time. Additionally these fields are traditionally not indexed in anyway.
Try to see if there are any indexes worth using instead or other joins.
Also your join to the I.ITEMTABL field is not required as the D.DESCTBL field has a filter making the processor work more to join the two, unless it's an index.
Another method would be to use a subquery in your where clause like:
SELECT D.DESCITEM, D.LONGDESC, D.DESCTABL, D.DESCCOY, D.DESCPFX
FROM VM1DTA.DESCPF D
WHERE D.DESCPFX = 'IT'
AND D.LANGUAGE = 'E'
AND D.VALIDFLAG = '1'
AND D.DESCTABL = 'T1680'
AND EXISTS (SELECT NULL
FROM VM1DTA.ITEMPF I
WHERE I.VALIDFLAG = '1'
AND I.ITEMTBL = 'T1680'
AND D.DESCITEM = I.ITEMITEM
AND D.DESCCOY = I.ITEMCOY)
ORDER BY LONGDESC ASC;