March 31, 2009 at 7:32 pm
I was looking at an old SP and noticed it's doing a CONVERT of dissimilar data types;
select ...........
FROM leads l
LEFT JOIN call_detail c ON l.rwa_id = CONVERT(nchar(10), c.rwa_id)
The odd thing is that l.rwa_id is not nchar, it's char, so the convert is wrong ... possibly a typo? Would there be a performance hit as-is converting c.rwa_id (int) to nchar instead of char ?? I assume I should change it, but am curious about it the way it is.
April 1, 2009 at 5:49 am
If you're comparing two different data types, char & nchar, then you'll get an implicit convert in the engine which will prevent the use of indexes. So yes, there is a performance hit. If both columns are char, converting to nchar must be a mistake. I'd remove it.
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April 1, 2009 at 12:17 pm
Hi
By looking at the query i am sure one wold want o have index in the ID column. So if you place any functions that then that would certainly hit performance.
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