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coalesce and nullif


coalesce and nullif

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Hugo Kornelis
Hugo Kornelis
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forjonathanwilson (6/23/2010)
null date can be cast as null string, but not the other way, interesting.Hehe

This is not correct. A null string can be cast as date (result will be NULL). The problem starts when you try to case a non-null string as date - in that case, the string must evaluate to a valid date. And obviously, the string 'Test' does not qualify there.


Hugo Kornelis, SQL Server MVP
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forjonathanwilson
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Hugo Kornelis (6/23/2010)
forjonathanwilson (6/23/2010)
null date can be cast as null string, but not the other way, interesting.Hehe

This is not correct. A null string can be cast as date (result will be NULL). The problem starts when you try to case a non-null string as date - in that case, the string must evaluate to a valid date. And obviously, the string 'Test' does not qualify there.


thanks for clarifying that for me. I also checked this myself after I made my irroneous assumption:

declare @c varchar(10), @c1 varchar(10),
@d datetime, @d1 datetime
select @c = 'test', @c1 = null, @d = '1/1/10', @d1 = null

select coalesce(nullif(@c,@c),nullif(@d,@d))

select coalesce(nullif(@d,@d),nullif(@c,@c))

where the results are compared null datetime to null string by coalesce, which completes just fine.
UMG Developer
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Interesting question, thanks.

Thanks Oleg for the explanation of why it happens, I think most people don't already know that, so it is very helpful.
ColdCoffee
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Oleg and Hugo , thanks for the nice explanations and links.. nice question depicting the precedence of data-types... niceee.
Anam Verma
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thanks for the good QOTD and explanation behind it.
Daniel Bowlin
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Good question, thanks. The answer logic seems backwards to me. I think I am going to have to do a little more reading.
SQLRNNR
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Excellent question



Jason AKA CirqueDeSQLeil
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MCM SQL Server, MVP


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Yuvaraj S-467280
Yuvaraj S-467280
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interesting qotd...thanks for enlighting on the difference

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Tom Thomson
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Fun question.

Tom

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