Interesting SQL ISNULL behavior

Found an interesting post about the SQL ISNULL function.  Apparently, it behaves differently if you’re using it to test strings.  For example:

DECLARE @a VARCHAR(100)
DECLARE @b VARCHAR(10)

SET @a=’This is much longer than 10 characters
SET @b=NULL

— This will display
—        This is mu

SELECT ISNULL(@b,@a)

— This will display
—        This is much longer than 10 characters

SELECT ISNULL(CONVERT(NVARCHAR(MAX), @b), @a)

Knowing this could keep you from pulling your hair out trying to investigate a bug when the truncated data gets down the pipeline.  Hope that helps someone out there.

Happy Coding!

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