Sunday, June 19, 2022

Case expressions may only be nested to level %d

Msg 125, Level 15, State 1, Line 1
Case expressions may only be nested to level %d.

I never experienced this in SQL Server 2017 onwards, but this was being experienced in previous version on Linked Server only. So below example is the demonstration of that assuming linked server.

Declare @id as int
set @id=13
    (CASE @Id
        WHEN 1 THEN 1
        WHEN 2 THEN 2
        WHEN 3 THEN 3
        WHEN 4 THEN 4
        WHEN 5 THEN 5
        WHEN 6 THEN 6
        WHEN 7 THEN 7
        WHEN 8 THEN 8
        WHEN 9 THEN 9
        WHEN 10 THEN 10
        WHEN 11 THEN 11
	WHEN 12 THEN 12
        WHEN 13 THEN 13
        WHEN 14 THEN 14
    END) AS Test
	from [SANTANA\MSSQLSERVER17].Rohit.dbo.Emp

You can resolve this by using below technique.

Using multiple coalesce cases.
Using Open query.

Points to remember :
  • The above query will work absolutely fine if you run from the local instances even more than 10 conditions.this error message only happens when we are applying a case from data that comes from a Linked Server.
  • If the query does not use Linked Server, you do not need to use this technique. You can use as many conditions as you want in the same case.
  • If your query uses Linked Server that points to its own instance, you do not need to use this technique either. It works like a normal query without linked server.
  • The COALESCE function accepts multiple conditions, so it is not limited to just 2 cases, they can be multiple (although the complexity of the code is increasing.)
  • You can only use up to 9 conditions in each CASE in scenarios where the query is done on remote data.
  • Using ELSE NULL at the end of each case is optional.
  • Subquery and CTE do not resolve this issue.
  • OPENQUERY and OPENROWSET do not have this limitation of 10 CASE conditions either.

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