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From Jeffrey Lichtman <swa...@rcn.com>
Subject Re: What is performance differenc(es) between 1 index per column or one index for multiple column?
Date Tue, 10 Jan 2006 04:48:58 GMT

>Thank you very much for reading my post.
>can you please explain me what is differences between 1 index for 
>one column and one index for multiple columns ?

In addition to what Ryan Bobko has already said about SELECT 
statements, I should point out that the existence of indexes on a 
table affects the performance of updates on the table. For example, 
if you have three indexes on a table, each insert of a row into the 
table will result in inserts into the three indexes as well as the 
base table. Same with deletes - each row deleted from the table must 
be deleted from the indexes as well. For UPDATE statements, the 
indexes are updated only if the index columns are updated, so with 
three indexes on a table an UPDATE statement could result in zero, 
one, two or three indexes being updated.

                        -        Jeff Lichtman
                                 Check out Swazoo Koolak's Web Jukebox at

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