You can use ISNULL(....)
SET @Concatenated = ISNULL(@Column1, '') + ISNULL(@Column2, '')
If the value of the column/expression is indeed NULL, then the second value specified (here: empty string) will be used instead.
You can use ISNULL(....)
SET @Concatenated = ISNULL(@Column1, '') + ISNULL(@Column2, '')
If the value of the column/expression is indeed NULL, then the second value specified (here: empty string) will be used instead.