问题
I try to create standardized SQL scripts for use in my SSRS reports. If I wish to have a statement such as:
Select * from mytable
and use a SQL Variable (SSRS parameter) in the where clause, is there any speed advantage to using this:
Where field = @MyField
VS.
Where field IN (@MyField)
I know the second option supports both multiple selections and single selections while the first supports only single.
Are there any performance hits if I write all my queries with the IN statement for uniformity?
回答1:
There is no performance hit. The optimizer converts the IN to a series of = operations ORed together.
As a side note, I hope you're not really using SELECT * in your actual queries.
回答2:
For one argument optimizer will change that IN into =, in real execution statement.
As both of this arguments are Sargeble (Joe Stefanelli thanks for attention); the difference in performance may by found where you have sequence value in in clause, for example IN (1,2,3,4,5,6) is slower that between 1 and 6, because for the IN the index has to be read for each value in this case 6 time for between only once.
回答3:
the performance does get slow if you have a large no of item in your IN clause
来源：https://stackoverflow.com/questions/3407577/in-vs-in-where-clauses