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webfred
Master Smack Fu Yak Hacker
8781 Posts |
 Posted - 2010-04-19 : 08:32:38
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Dear all,SELECT ...UNION ALLSELECT ...UNION ALLSELECT ...My colleague has this issue.If all 3 selects do return at leat one record then the select needs 4 secs.If one select doesn't return data then the select needs 1 minute.Has someone else of you ever had this problem?Is there a known reason?Is there a trick to make it better?ThanksFred
No, you're never too old to Yak'n'Roll if you're too young to die. |
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harsh_athalye
Master Smack Fu Yak Hacker
5581 Posts |
Posted - 2010-04-19 : 08:39:14
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| What time does it take when you individually run those 3 statements? Does it take time when no data is returned for that particular statement?Harsh Athalyehttp://www.letsgeek.net/ |
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webfred
Master Smack Fu Yak Hacker
8781 Posts |
Posted - 2010-04-19 : 08:53:31
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With UNION ALL if one select doesn't return data then the select needs 1 minute.Same statement and the UNION ALL lines commented out --> 4 secs.
No, you're never too old to Yak'n'Roll if you're too young to die. |
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Kristen
Test
22859 Posts |
Posted - 2010-04-19 : 09:18:55
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| Could it be that when the "problem" UNION returns rows the query plan uses an Index, but when it doesn't then the query plan does a Table Scan instead?? |
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UNION ALL slow if one select returns no data