1=1 Usage and performance

1=1 usage and performance

Fuse: Found some where and JOIN on statements with 1=1 conditions in the optimized stored procedure .

Why do you use the WHERE 1=1

to facilitate the stitching of SQL conditions :

Instance:

DECLARE @SQL1 NVARCHAR (max), @SQL2 NVARCHAR (max), @CLASSID intset @CLASSID =2select @SQL1 = ' SELECT * from w_question WHERE 1 = 1 ' IF ISNULL (@CLASSID, 0) <>0select @[email protected]+ ' and classid= ' +convert (NVARCHAR), @CLASSID)

The final splicing statement is:

SELECT * from W_question WHERE 1=1 and classid=2

If not the conditions of the 1=1 will appear:

SELECT * from W_question WHERE and classid=2

Or:

SELECT * from W_question WHERE

Such an SQL statement, causing an error

WHERE 1=1 has an impact on performance

because the query parser filtered the 1=1 directly in the algebraic tree optimization phase. , so 1=1 has no effect on performance.

Instance:

SELECT * from W_questionselect * from W_question WHERE 1=1

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1=1 Usage and performance