I am looking at implicit conversions in my stored procedures and the biggest one I have in my prod database is a warning by the Cardinality Estimator in SQL 2014 for converting datetime to formatted date.

I have read the following questions: Warning in query plan "Cardinality Estimate" and DateTime to Format: Implicit Conversion but these fail to mention that FORMAT() removes the warning they are only describing that the problem won't be fixed, which is not a solution I looking for, FORMAT() is a viable solution.

Previously we used the formatting option on CONVERT() to format the date, but ANYTIME I use CONVERT() I get an implicit conversion.

CREATE TABLE #temptable ( [Birthdate] datetime )
INSERT INTO #temptable
( N'1891-12-30T00:00:00' ), 
( N'1918-10-31T00:00:00' ), 
( N'1917-12-21T00:00:00' ), 
( N'1906-10-29T00:00:00' ), 
( N'1916-12-12T00:00:00' ), 
( N'1916-11-08T00:00:00' ), 
( N'1918-10-01T00:00:00' ), 
( N'1913-03-18T00:00:00' ), 
( N'1920-08-03T00:00:00' ), 
( N'1919-10-22T00:00:00' )

SELECT CONVERT(VARCHAR(26),t.Birthdate,109) AS varConvert,
        CONVERT(NVARCHAR(26), t.Birthdate, 109) AS nvarConvert,
        TRY_CONVERT(VARCHAR(26),t.Birthdate, 109) AS tryCon,
        FORMAT(t.Birthdate, 'MMM dd yyyy') AS form
FROM #temptable AS t

DROP TABLE #temptable

The only not implicit conversion to a formatted date is the FORMAT() function:

enter image description here

Is there a way to not use the FORMAT() function and continue using the Convert function to return formatted dates? Ie do i need to extend or reduce the length of my formatted dates during conversion. I want to avoid implicit conversions, but re-writting all CONVERT() to FORMAT() will take more testing than changing the current CONVERT functionality.


1 Answer 1


The query you posted does indeed produce PlanAffectingConvert warnings in SQL Server 2016 SP1 (didn't try on earlier versions).

That's a bug - those convert statements shouldn't be throwing that warning since it doesn't affect cardinality in any way when they're just in the SELECT portion.

File a bug report for it at http://connect.microsoft.com and include your repro code, and edit your question to include a link to the Connect item so folks can upvote it.


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