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Posts Tagged ‘sql server query hint’

Quick one today:

In the past, we’ve covered a MAXDOP query hint with details and nuances (and here too). This time, we’ll get into another interesting query hint MAXRECURSION.

One of my colleagues needed to come up with a numbers table with values like this, where there are multiple batches and each batch has some records.

Batch RecordsInBatch
1 1
1 2
1 3
1 4
1 2500
2 1
2 2
.. ..
2 2500
.. ..
999 2500

This could be achieved with recursive CTE with a table OPTION (MAXRECURSION = n).

--
--  Numbers table with recursive CTE
--
DECLARE @BN INT = 999, @RN INT = 2500

;WITH BatchNumbers (BatchNum)
AS	(
		SELECT 1 AS BatchNum
		UNION ALL
		SELECT BatchNum + 1 AS BatchNum
		FROM BatchNumbers
		WHERE BatchNum < @BN
	),
RecordNumbers (RecNum)
AS	(
		SELECT 1 AS RecNum
		UNION ALL
		SELECT RecNum + 1 AS RecNum
		FROM RecordNumbers
		WHERE RecNum < @RN
	)
SELECT BatchNumbers.BatchNum, RecordNumbers.RecNum
FROM RecordNumbers
CROSS JOIN BatchNumbers
ORDER BY BatchNumbers.BatchNum, RecordNumbers.RecNum
OPTION (MAXRECURSION 2500)
GO

MAXRECURSION – points to keep in mind

  • Server-wide, the limit is set to 100.
    • Use MAXRECURSION query hint to prevent infinite loops
  • Server-wide default is set to 100
  • When MAXRECURSION 0 is specified, it is same as infinite loops (no limit)
  • In query hint, values for MAXRECURSION range from 0 to 32,767
  • In cases where incorrect code enters into production, that results in infinite loops, MAXRECURSION could be used to limit the loops.
Hope this helps,
_Sqltimes

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