Question on Select

[Alex]

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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[Rajesh Kumar Mallah]

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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