>>I'll try later - busy with work right now. I tried on the tables I had in my test database (in SQL Server).
>
>Ok I just tried for you:
>

                                                    t6   t5   t4   t3   t2   t1
>Client processing time         0    0    0    0    0   16 
>Total execution time        2328 2296 3046 2250 2328 5937 
>Wait time on server replies 2328 2296 3046 2250 2328 5921 
>

>
>Two passes. t1,4 (LEFT), t2,5 (NOT IN), t3, 6 (Exists).
>Cetin

In your tests performance of the LEFT JOIN seems to be much worse than others. What are tables metrics and how many records did you get as a result of a query? Also, did you discharge the results or not?