select ref_code from tab_b where not exists (select * from tab_a where
item_id = tab_b.item_id);
make sure u have index on item_id in tab_a .
the above sql is quite efficient , other method is to use left join.
Alex wrote:
> Hi,
> I have two tables,
> Table A: item_id
> Table B: item_id, ref_code
> and i want to list all ref_codes in table B that are not referenced
> by Table A.
> Table A has about 3million records./ table B 200
>
> What is the best way to do that ?
>
> Thanks
> Alex
>
>
>
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