Violation of %ls constraint '%.*ls'. Cannot insert duplicate key in object '%.*ls'.

Error Message:
Msg 2627, Level 14, State 1, Line 10
Violation of %ls constraint '%.*ls'. Cannot insert duplicate key in object '%.*ls'.

Severity level:
14.

Description:
This error message appears when you try to insert an already existing value into a column for which a PRIMARY KEY or UNIQUE constraint was declared.

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

Resolution:
Error of the Severity Level 14 are generated by the user and are corrigible by the user. The statement cannot be executed this way. Duplicate key values are not allowed in columns for which a PRIMARY KEY or UNIQUE constraint was created. The data cannot be inserted.

Versions:
All versions of SQL Server.

Example(s):
USE tempdb;
IF OBJECT_ID('tempdb..#t') > 0
 DROP TABLE #t
CREATE TABLE #t
(
 c1 INT PRIMARY KEY
)

INSERT INTO #t SELECT 1
INSERT INTO #t SELECT 1

Remarks:
In the above example we try to insert twice a value of 1 into the column c1 of the table #t. Because there exists a PRIMARY KEY constraint for this column, the error is raised.