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I have a sql query that runs super fast, around one second, when not using variables, like:
WHERE id BETWEEN 5461094 and 5461097 But when I have:
declare @firstId int declare @lastId int set @firstId = 5461094 set @lastId = 5461097 ... WHERE id BETWEEN @firstId and @lastId … the query runs really slow, finishing only after some minutes. Why does it happen? I need to use variables. Can I do any improvement to avoid this performance problems?
It’s because when the values are hard coded, it can look up the statistics it has on the data in the table, and figure out the best query to run. Have a look at the execution plans of each of these queries. It must be scanning when your using variables.
if the range is always small you might be able to use an index hint to help this.