SQL2005: Simple query performance on column with nulls

[aconybeare]

Hi,

I'm having performance problems with a query on a table with loads of nulls in a particular column. I've tried changing the nulls to 0 (Zero) and rebuilt the index on the column but it's not really helped.

The table only has about 350K rows this first query returns in less than a second, the MS_No column is largely populated but is nullable.

	SELECT Corresp_Id
	FROM Correspondence c 
	WHERE c.Deleted=0
	AND c.Jnl_Code=@Jnl_Code
	--AND c.Mtg_Id=@Mtg_Id
	AND c.MS_No='MTG2011/0000016'
	ORDER BY Corresp_Id DESC;

This query on the same table but accessing a different column takes about 7 seconds.

	SELECT Corresp_Id
	FROM Correspondence c 
	WHERE c.Deleted=0
	AND c.Jnl_Code=@Jnl_Code
	AND c.Mtg_Id=@Mtg_Id
	--AND c.MS_No='MTG2011/0000016'
	ORDER BY Corresp_Id DESC;

Does anyone have any ideas on how to improve the performance of this query?

Regards Al