SQL statement to check for empty string - T-SQL - sql

Question

I am trying to write a WHERE clause for where a certain string variable is not null or empty. The problem I am running into is that certain non-empty strings equal the N'' literal. For instance:
declare #str nvarchar(max) = N'㴆';
select case when #str = N'' then 1 else 0 end;
Yields 1. From what I can gather on Wikipedia, this particular unicode character is a pictograph for submerging something, which is not semantically equal to an empty string. Also, the string length is 1, at least in T-SQL.
Is there a better (accurate) way to check a T-SQL variable for the empty string?

Answer 1

I found a blog, https://bbzippo.wordpress.com/2013/09/10/sql-server-collations-and-string-comparison-issues/
which explained that
The problem is because the “default” collation setting
(SQL_Latin1_General_CP1_CI_AS) for SQL Server cannot properly compare
Unicode strings that contain so called Supplementary Characters
(4-byte characters).
A fix is to use a collation that doesn't have problems with the supplementary characters. For example:
select case when N'㴆' COLLATE Latin1_General_100_CI_AS_KS_WS = N'' then 1 else 0 end;
will return 0. See the blog for more examples.
Since you are comparing to the empty string, another solution would be to test the string length.
declare #str1 nvarchar(max) =N'㴆';
select case when len(#str1) = 0 then 1 else 0 end;
This will return 0 as expected.
This also yields 0 when the string is null.
EDIT:
Thanks to devio's comment, I dug a bit deeper and found a comment from Erland Sommarskog https://groups.google.com/forum/#!topic/microsoft.public.sqlserver.server/X8UhQaP9KF0
that in addition to not supporting Supplementary Characters, the Latin1_General_CP1_CI_AS collation doesn't handle new Unicode characters correctly. So I'm guessing that the 㴆 character is a new Unicode character.
Specifying the collation Latin1_General_100_CI_AS will also fix this issue.