Column ‘%.*ls’ in table ‘%.*ls’ is of a type that is invalid for use as a key column in an index.

Error Message:
Msg 1919, Level 16, State 1, Line 1
Column ‘%.*ls’ in table ‘%.*ls’ is of a type that is invalid for use as a key column in an index.

Severity level:
16.

Description:
This error message appears when you try to create an index on (a) column(s) of invalid data types for an index.

Consequences:
The T-SQL statement can be parsed, but causes the error at runtime.

Resolution:
Error of the Severity Level 16 are generated by the user and can be fixed by the SQL Server user. The statement cannot be executed this way. The data types for the underlying columns must be changed in order to create the index.

Versions:
All versions of SQL Server.

Example(s):
USE tempdb;
GO
IF OBJECT_ID(‘tempdb..#t’) > 0
 DROP TABLE #t
GO
CREATE TABLE #t
(
 id INT NULL,
 c1 TEXT
 CONSTRAINT unq_working UNIQUE
)
GO

Remarks:
In the above example we try to create a UNIQUE constraint on a column of the TEXT data type. Because SQL Server create internally an index to enforce the constraint, the error is raised.




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