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sixsigma1978
Starting Member
25 Posts |
 Posted - 2011-09-19 : 12:49:25
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| Basic question : Am trying to get a picture of what really happens when, say, a where clause is called on a column in an Indexed vs Non-Indexed scenario.Specifically, in the case of non-clustered index.So if we search on table with a query WHERE UnitPrice> 15.If the table is non-indexed, naturally, the column is used - but in case the column is indexed -> What does the query scan perform on? Is the index literally a separate "temp" column which points to each row in table and the WHERE occurs on this temp column? very elementary question - but I'm trying to get a picture of how a table select works physically! |
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visakh16
Very Important crosS Applying yaK Herder
52326 Posts |
Posted - 2011-09-19 : 12:54:16
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| yep. provided it has non clustered index it means there's a separate index table available with index values and pointer to clustered index position of record. Then optimiser will determine whether its easier to traverse the index than to traverse main clustered index and then depending on that it might get index seek,scan or clustered index scan.------------------------------------------------------------------------------------------------------SQL Server MVPhttp://visakhm.blogspot.com/ |
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GilaMonster
Master Smack Fu Yak Hacker
4507 Posts |
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sixsigma1978
Starting Member
25 Posts |
Posted - 2011-09-19 : 16:27:41
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| thanks - this was helpful! cheers |
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Where do indexes physically reside?