Cannot create the clustered index "%.*ls" on view "%.*ls" because the select list of the view definition does not include all columns in the GROUP BY clause. Consider adding these columns to the select list.

Error Message:
Msg 8660, Level 16, State 0, Line 2
Cannot create the clustered index "%.*ls" on view "%.*ls" because the select list of the view definition does not include all columns in the GROUP BY clause. Consider adding these columns to the select list.

Severity level:
16.

Description:
This error message appears when you try to create a clustered index on a view, but not all columns in the GROUP BY clause are also contained in the 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. All columns in the GROUP BY list must also be contained in the SELECT list.

Versions:
This error message was introduced with SQL Server 2000.

Example(s):
SET NUMERIC_ROUNDABORT OFF;
SET ANSI_PADDING,
    ANSI_WARNINGS,
    CONCAT_NULL_YIELDS_NULL,
    ARITHABORT,
    QUOTED_IDENTIFIER,
    ANSI_NULLS ON;
GO

IF OBJECT_ID ('dbo.v', 'View') IS NOT NULL
   DROP VIEW dbo.v;
GO

IF OBJECT_ID('dbo.t') IS NOT NULL
    DROP TABLE dbo.t;
GO

CREATE TABLE dbo.t
(
    c1 int NOT NULL
);
GO

CREATE VIEW dbo.v
WITH SCHEMABINDING
AS
SELECT
    SUM(T.c1) AS c1, COUNT_BIG(*) AS MyCount
FROM
    dbo.t T
GROUP BY
    T.c1;
GO

CREATE UNIQUE CLUSTERED INDEX cix_v
    ON dbo.v (c1);
GO

Remarks:
In the above example we try to create an index on a view. Since the column c1 of the base table is contained in the GROUP BY list but not in the SELECT list, the error is raised.