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sqlclarify
Yak Posting Veteran
56 Posts |
 Posted - 2008-09-20 : 21:54:47
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| Hello,I have a query of the formselect * from(select col1,col2,col3 from table a where xxx = '100') der1join(select * from der1)der2on der1.pk = der2.pkI get der1 is invalid table.How do I use a derived table in another derived table? Is it not possible? |
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TG
Master Smack Fu Yak Hacker
6065 Posts |
Posted - 2008-09-20 : 23:24:13
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| >>Is it not possible?Not like that, no.You should not get too "derived table" happy. The Optimizer will not be able to take advantage of indexes, statistics, etc. with derived tables. It can be an effective tool to significantly reduce the number or rows being JOINed but your example is not valid and would not be an effective technique if it was valid.2005 has a new feature: Common Table Expressions (CTE) which allow referencing a derived table multiple times.Be One with the OptimizerTG |
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derived table scope