Recursive common table expression ‘%.*ls’ does not contain a top-level UNION ALL operator.

Error Message:
Msg 252, Level 16, State 1, Line 1
Recursive common table expression ‘%.*ls’ does not contain a top-level UNION ALL operator.

Severity level:
16.

Description:
This error message appears when a Common Table Expression does not contain a top-level UNION ALL operator.

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 CTE must contain a top-level UNION ALL operator.

Versions:
This error message was introduced with SQL Server 2005.

Example(s):
USE tempdb;
GO
IF OBJECT_ID(‘tempdb..#t’) > 0
 DROP TABLE #t
GO
CREATE TABLE #t
(
 id INT,
 reportToID INT NULL,
)
INSERT INTO #t SELECT 1, NULL
UNION ALL SELECT 2, 1
UNION ALL SELECT 3, 1
UNION ALL SELECT 4, 2
GO
WITH MyCTE (id, reportToID, Level)
AS
(
 SELECT t1.ID, t1.reportToID, Level + 1
   FROM #t AS t1
   JOIN MyCTE AS t2
     ON t1.reportToID = t2.ID
)
SELECT *
  FROM MyCTE
GO

Remarks:
In the above example we try to create a CTE without a UNION ALL operator on the top-level. This raises the error.




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