1. Instead of multiple OR use IN operator.

2. The NOT IN subquery performs much better when re-written as LEFT JOIN as

select myField where myField not in (select myField from another table)

would be much quicker as

select myTable.myField LEFT JOIN AnotherTable on myTable.MyField = AnotherTable.myField where AnotherTable.PK IS NULL




>The following query runs optimized:
>
>

>SELECT Temp.AddDate,Thread.NoThread,Thread.Title
> FROM (SELECT TOP 10 MIN(Thread.NoThread) AS NoThread,MAX(Thread.AddDate) AS AddDate,MAX(Thread.Numero) AS Numero
> FROM Thread
> WHERE Thread.AddDate>ldDate AND Thread.NoParent=0 AND (Thread.NoClient=44 OR Thread.NoClient=99 OR Thread.NoClient=51 OR 
> Thread.NoClient=37 OR Thread.NoClient=10 OR Thread.NoClient=39 OR Thread.NoClient=32 OR Thread.NoClient=41 OR Thread.NoClient=16 OR 
> Thread.NoClient=24 OR Thread.NoClient=50 OR Thread.NoClient=29 OR Thread.NoClient=28 OR Thread.NoClient=33 OR Thread.NoClient=38 OR 
> Thread.NoClient=36 OR Thread.NoClient=35 OR Thread.NoClient=21 OR Thread.NoClient=17 OR Thread.NoClient=5 OR Thread.NoClient=9 OR 
> Thread.NoClient=42 OR Thread.NoClient=52)
> GROUP BY Thread.NoThread ORDER BY 2 DESC) Temp
> INNER JOIN Thread ON Temp.NoThread=Thread.Numero
> ORDER BY Temp.AddDate DESC
>

>
>But, if I add a condition in it for a sub query, it is slow.
>
>

>SELECT Temp.AddDate,Thread.NoThread,Thread.Title
> FROM (SELECT TOP 10 MIN(Thread.NoThread) AS NoThread,MAX(Thread.AddDate) AS AddDate,MAX(Thread.Numero) AS Numero
> FROM Thread
> WHERE Thread.AddDate>ldDate AND Thread.NoParent=0 AND (Thread.NoClient=44 OR Thread.NoClient=99 OR Thread.NoClient=51 OR 
> Thread.NoClient=37 OR Thread.NoClient=10 OR Thread.NoClient=39 OR Thread.NoClient=32 OR Thread.NoClient=41 OR Thread.NoClient=16 OR 
> Thread.NoClient=24 OR Thread.NoClient=50 OR Thread.NoClient=29 OR Thread.NoClient=28 OR Thread.NoClient=33 OR Thread.NoClient=38 OR 
> Thread.NoClient=36 OR Thread.NoClient=35 OR Thread.NoClient=21 OR Thread.NoClient=17 OR Thread.NoClient=5 OR Thread.NoClient=9 OR 
> Thread.NoClient=42 OR Thread.NoClient=52) AND
> Thread.Numero NOT IN (SELECT Thread2.NoParent FROM Thread AS Thread2 WHERE Thread.Numero=Thread2.NoParent)
> GROUP BY Thread.NoThread ORDER BY 2 DESC) Temp
> INNER JOIN Thread ON Temp.NoThread=Thread.Numero
> ORDER BY Temp.AddDate DESC
>

>
>How can I adjust it so it would be optimized?