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kmansoor
Starting Member
2 Posts |
 Posted - 2011-12-30 : 12:54:01
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| Hi All- I understand a correlated query uses values from the outer/containing query. Joe Celko, in 'SQL for smarties' says it is a way to hide loops in SQL.My question: What kind of problems are generally solved using correlated subqueries? is there a 'way' for me to discern 'right away' this problem will need a correlated sub-query to solve? |
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sunitabeck
Master Smack Fu Yak Hacker
5155 Posts |
Posted - 2011-12-30 : 17:10:28
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| I don't know if there is a litmus test that can let one discern whether to use subqueries or not. But, subqueries are useful when you want to evaluate something for each row in the outer query - a brief description on MSD alludes to that: http://msdn.microsoft.com/en-us/library/ms187638.aspxAfter I read your posting, I was thinking about how *I* decide how to write a query; i.e., how I decide what features of T-SQL to use, or what methodology to use. I am really unable to answer it - I just don't know. When I see the problem, I sort of know what technique might fit that problem, and go with that. And a lot of times, that "shooting from the hip" approach ends up being not the best approach. So then I rework it to make it better.More experienced and skilled SQL experts on this forum may have systematic ways of approaching a problem. If they do, I don't know what those are. |
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kmansoor
Starting Member
2 Posts |
Posted - 2011-12-30 : 22:35:50
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| Hi- Thank you for replying, one clarification:What type of problems a 'Correlated Sub-query' solves? when would one use a correlated sub-query instead of a regular sub-query? |
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Correlated subquery -- higher level of abstraction