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Sort operation in execution plan


Sort operation in execution plan

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yuvipoy
yuvipoy
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I have two set of tables
each table has unique Column and indexes.
while doing a Order by operation when i issue order by columns in one table i dont see any Sort operation cost(less than 15%), where as if i include second table column in the order by then the Sort operation cost is nearly 70%
so what might be the reason ?
Koen Verbeeck
Koen Verbeeck
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Without any table DDL, index definitions, queries used and query plan we can only guess.

Maybe because in the first query data was already presorted by an index, while in the second query the index could not be used to sort the data and thus it had to do more work?


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yuvipoy
yuvipoy
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Thanks for your answer. let me look and come with necessary details.
Grant Fritchey
Grant Fritchey
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Pretty sure Koen has nailed it already. The JOIN is likely to change the order in which data is retrieved, so a sort operation will be necessary.

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