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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