why in operator is very slow in run time?

[Pernia]

Hello,

This sql query is very slow in runtime and takes a long time to return the result, because of the in operator inside query(because the second table includes more than 10000 records)
i think i have to change it by using Join commands to increase the speed in runtime.

but how do i rewrite the following command to turn the Join Command?

Select distinct Fit_R_id from Wels
where Fit_R_id is not null 
and 
id not in
(
select Wels_id from Fit
)

i tried this :

Select distinct  Fit_R_id from Wels
left  JOIN Fit ON wels.id = fit.wels_id
where
wels.fit_R_id is not null 
GROUP BY wels.fit_R_id

but the result was not equal to the first query!
what is answer?
thanx

[June7]

Don't think you need both DISTINCT and GROUP BY.

You want to know which IDs in fit are not in wels? WHERE wels.fit_R_id Is Null

Did you use the FindUnmatched query wizard?