RE: multiple index on same column

SSC Guru

Points: 186127

May 12, 2015 at 9:28 am

andrew_dale (4/30/2015)
many thanks for the replies, they do make sense.
checking the execution plan, if I run a simple query and include one of the index fields in the where clause then I get Clustered Index Seek if the where is on yps_ayrc and a Clustered Index Scan if the where is on yps_pslc
If I write a more complicated query, with a group by on yps_pslc, then it does a NonClustered Index Scan on ins_ypsI3

Don't forget to exclude from your query any columns which are not in the index. SELECT * FROM ... WHERE .. will almost always require reads from the clustered index. SELECT 1 FROM ... WHERE ... would be appropriate to use for this test, or better still, add only the columns which appear in the WHERE clause to the SELECT list.

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

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