Column names in each view or function must be unique. Column name '%.*ls' in view or function '%.*ls' is specified more than once.

Error Message:
Msg 4506, Level 16, State 1, Procedure v, Line 4
Column names in each view or function must be unique. Column name '%.*ls' in view or function '%.*ls' is specified more than once.

Severity level:
16.

Description:
This error message appears when you try to create a view or function that has non-unique column names in its SELECT list.

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 are corrigible by the user. The statement cannot be run this way. Column names in the SELECT list of a view or function must be unique.

Versions:
All versions of SQL Server.

Example(s):
IF OBJECT_ID ('dbo.v') IS NOT NULL
    DROP VIEW dbo.v;
GO

CREATE VIEW dbo.v
AS
SELECT
    1 AS c1,
    2 AS c1
GO

Remarks:
In the above example we try to create a view in which we try to specify the column name c1 twice. This raises the error.