Dealing with nulls in SQL Server

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Adding null values to a variable can produce different results based on a SQL Server setting. Look at the statement, "Set concat_null_yields_null off" in the code below.

This tells SQL Server to ignore the null value and display the sum of the non-null variables as the result. Thus, the result in this example will be 'hello.'

If you change the code to use

set concat_null_yields_null on

Then the result will always be null since SQL Server will now no longer ignore the null variable and treat anything added to null as NULL.

declare @var1 varchar(10)
declare @var2 varchar(10)

set concat_null_yields_null off

set @var1='hello'
set @var2=null

print @var1+@var2

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This was first published in June 2005

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