thanks chris,
This took much longer. I think it did not like outer join !!
Any ways, after you replied I realized that I can use MINUS which work at lightning speed.

Select ProjectCode_Item_Code
FROM mwebProjectCode
MINUS
SELECT Work_Item_Code
FROM mwebWork
WHERE Work_Entity_Type = 3
AND Work_ID <> 2531
AND Work_Level= 6
order by ProjectCode_Item_Code ;
Thanks again