>>Hi
>>
>>I'm extracting some records and I want to exclude some of them from being extracted.
>>
>>So I say
>>

>>SELECT * from member 
>>where individual ref not in (select individual_ref from attribute where attribute.attr_code_ref = 1242 and individual_ref is not NULL and valid_to < getdate())
>>

>>Is that the best way of doing this. ?
>>
>>Thanks
>
>You can find the best way if you turn Actual Execution plan on and test several different queries and check what is faster.
>I prefer to write it with LEFT JOIN but this could be slower than yours, also the is NOT EXISTS() clause.
>Check them all and choose faster :-).

My preference is NOT EXISTS subquery. Gail Shaw wrote a blog on this topic and in her analysis NOT EXISTS was the winner.