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Which is better (Case, IsNull, COALESCE)


Which is better (Case, IsNull, COALESCE)

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drbob
drbob
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1. Case When mycolumn IS Null Then 0 Else mycolumn END As mycolumn
OR
2. IsNull(mycolumn,0) As mycolumn
OR
3. COALESCE(mycolumn,0) As mycolumn
mister.magoo
mister.magoo
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In this case, I would plump for 2.

Reason 1 : #1 and #3 are the same behind the scenes, but #3 is shorter and more readable, so eliminate #1
Reason 2 : ISNULL will convert your default value of zero to whatever datatype myColumn has, which in this case would be preferable.
Reason 3 : COALESCE can evaluate the expressions being coalesced more than once, which can lead to unexpected results.
Reason 4 : you are only handling one expression and a default value for null, so you don't need coalesce.

MM


select geometry::STGeomFromWKB(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  • drbob
    drbob
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    Thanks..
    So Do I understand correctly that coalesce would be best in a situation like this>
    COALESCE(myalpacolumn,mynumcolumn,mybinarycolumn,'') As mycolumn
    mister.magoo
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    I didn't say that ;-)

    ...but yes, generally I would advocate COALESCE for that use.

    MM


    select geometry::STGeomFromWKB(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  • Luis Cazares
    Luis Cazares
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    Remember to have in mind the data type that ISNULL and COALESCE return.
    ISNULL will try to convert the second expression to the data type of the first expression.
    COALESCE will convert all expressions to the expression with the highest data type precedence.


    Luis C.
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