String Type Conversion During Concatenation in SQL Server

Q

What Happens When Unicode Strings Concatenate with Non-Unicode Strings in SQL Server Transact-SQL?

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A

If a Unicode string NVARCHAR is concatenated with a non-Unicode string VARCHAR, SQL Server will implicitly convert the non-Unicode string to Unicode string for concatenation.

DECLARE @regcode VARCHAR(40);
DECLARE @unicode NVARCHAR(40);
SET @regcode = 'Some Unicode characters: '
SET @unicode = NCHAR(9733)+NCHAR(9734)+NCHAR(9792)
   +NCHAR(9794);
SELECT @regcode + @unicode; 
SELECT DATALENGTH(@regcode);
SELECT DATALENGTH(@unicode);
SELECT DATALENGTH(@regcode + @unicode);
Some Unicode characters: ????
25
8
58

Note that the non-Unicode string @regcode has been converted to a Unicode string. The number of bytes of @regcode changed from 25 to 50. With 8 bytes from @unicode, the number of bytes of the concatenated string becomes 58.

 

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2017-03-11, 322👍, 0💬