Question

I found this snippet of SQL in a view and I am rather puzzled by it’s purpose (actual SQL shortened for brevity):

SELECT
    COALESCE(b.Foo, NULL) AS Foo

FROM a
LEFT JOIN b ON b.aId=a.Id

I cannot think of a single reason of the purpose of coalescing with null instead of just doing this:

SELECT
    b.Foo AS Foo

FROM a
LEFT JOIN b ON b.aId=a.Id

Or at the very least don’t include the NULL explicitly:

SELECT
    COALESCE(b.Foo) AS Foo

FROM a
LEFT JOIN b ON b.aId=a.Id

I don’t know who authored this (so I cannot ask), when it was authored, or for what specific MS SQL Server version it was written for (pre-2008 for sure though).

Is there any valid reason to coalesce with NULL instead of just selecting the column directly? I can’t help but laugh and write it off as a rookie mistake but it makes me wonder if there is some “fringe case” that I don’t know about.

Answer 1

You are right – there is no reason to use:

SELECT COALESCE(b.Foo, NULL)

…because if b.foo is NULL, you might as well just use:

SELECT b.foo

…assuming that you want to know if the value is null.