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ISNULL vs COALESCE

Hello Experts;

Two questions, are the 2 queries below performing or giving the same results?  And, if so which one should I go with?  When I display the execution plans they are both identical.

Thanks

 SELECT (CASE WHEN (COALESCE(c1, '') = '') THEN '' ELSE COALESCE(c1, '') END ) AS c1,
        (CASE WHEN (COALESCE(c1, '') = '') THEN '' ELSE COALESCE(c2, '') END ) AS c2,
        (CASE WHEN (COALESCE(c1, '') = '') THEN '' ELSE COALESCE(c3, '') END ) AS c3,
        (CASE WHEN (COALESCE(c1, '') = '') THEN '' ELSE COALESCE(c4, '') END ) AS c4
        , Userid
        , ID
        , LID
   FROM Mant.dbo.View1
   
 SELECT ISNULL(c1, '') AS c1,
            ISNULL(c2, '') AS c2,
            ISNULL(c3, '') AS c3,
            ISNULL(c4, '') AS c4
            , Userid
        , ID
        , LID
    FROM Mant.dbo.View1
0
wdbates
Asked:
wdbates
3 Solutions
 
Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
The only big difference I've discovered between ISNULL and COALESCE is that ISNULL has only two parameters (value, value if null), whereas COALESCE can handle multiple parameters, returning the first non-null one it finds (value1, value2, value3, valueN)

No idea on performance.  I'd guess ISNULL would be quicker, but you'll have to test that yourself.
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Jim P.Commented:
The IsNull function can only handle one option. The Coalesce can handle multiple as in COALESCE(c1, c2, c3, c4,'') so it will pick the first non-null value.

So if there is just a need to display an empty string or a 0 then use the IsNull. The Coalesce is for checking against multiple choices. But as you are using them, there is no significant difference.
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John_VidmarCommented:
As stated by the previous experts, COALESCE is an ISNULL that allows for more than one NULL replacement.

I would hate to maintain something written by whoever wrote the 1st query... use the 2nd query.  In fact, you can take the 2nd query and replace ISNULL with COALESCE (all that stuff with CASE-statement in the 1st query is useless).
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wdbatesAuthor Commented:
Thank you all for the confirmation.
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Jim P.Commented:
Can I ask why a B grade?

What grade should I award?
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wdbatesAuthor Commented:
It's because I must have had a brain fart while driving the mouse.  I will ask for it to be changed.

thank you for catching my error.
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