Both a PRIMARY KEY and UNIQUE constraint have been defined for column '%.*ls', table '%.*ls'. Only one is allowed.

Error Message:
Msg 8151, Level 16, State 0, Line 1
Both a PRIMARY KEY and UNIQUE constraint have been defined for column '%.*ls', table '%.*ls'. Only one is allowed.

Severity level:
16.

Description:
This error message appears when you try to create both a PRIMARY KEY and a UNIQUE constraint on the same set of columns in a single statement.

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

Resolution:
Errors of the Severity Level 16 are generated by the user and are corrigible by the user. The statement cannot be executed this way. You cannot create both constraints in a single statement, but rather need to split them in to two separated statements.

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
 CONSTRAINT PK_t PRIMARY KEY
 CONSTRAINT UC_t_id UNIQUE
)
GO

Remarks:
In the above example we try upon table creation to create both a PRIMARY KEY and a UNIQUE constraint on the column id of the table #t. This raises the error.

In order to successfully execute the statement, you need to split the constraint creation into two separated statemtents like this:

USE tempdb;
GO
IF OBJECT_ID('tempdb..#t') > 0
 DROP TABLE #t
GO
CREATE TABLE #t
(
 id INT
 CONSTRAINT PK_t PRIMARY KEY
)
GO
ALTER TABLE #t
 ADD CONSTRAINT UC_t_id UNIQUE(id)