Er MS-SQL OG/ELLER betinget (udfør kortslutningsevaluering)?

Der er ingen garanti for denne adfærd.

Et eksempel på kortslutningsevaluering ikke sker med expr1 AND expr2 er

SET STATISTICS IO ON

IF EXISTS(SELECT COUNT(*) FROM master..spt_monitor HAVING COUNT(*)=2)  
AND EXISTS (SELECT COUNT(*) FROM master..spt_values HAVING COUNT(*)=1)
PRINT 'Y'

EXISTS(SELECT COUNT(*) FROM master..spt_monitor HAVING COUNT(*)=2) er false (betyder And -ed udtryk skal være False ), men IO-resultaterne viser, at den anden betingelse stadig blev evalueret.

Table 'spt_values'. Scan count 1, logical reads 14, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'spt_monitor'. Scan count 1, logical reads 1, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server kan gør dog dette. Jeg ser dette i min test

SET STATISTICS IO ON

DECLARE @p1 BIT = NULL

IF ( @p1 = 1
     AND EXISTS(SELECT *
                FROM   master..spt_values) )
  PRINT '1'

ELSE IF ( @p1 = 0
     AND EXISTS(SELECT *
                FROM   master..spt_values) )
  PRINT '2'

Udgangen er

Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(1 row(s) affected)
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

(1 row(s) affected)

Viser spt_values blev aldrig tilgået.

Dette implementeres ved en pass through-prædikatbetingelse i udførelsesplanen. Der er nogle oplysninger om dem her.