I folks.

I'm struggling with a select which should be easy.

select v_d_code, v_o_number, v_vin, v_status from vista_details where
v_d_code='64340' and v_o_number='C0023';
v_d_code | v_o_number | v_vin | v_status
----------+------------+-------------+-------------
64340 | C0023 | GCDW7D37645 | COMPOUND IN
(1 row)

shows that the record exists in vista.

select w_vin from walon where substring(w_vin from '(.{11}$)')
= 'GCDW7D37645';
w_vin
-------
(0 rows)

shows that it doesn't exist in walon.

So, who does this select not return the row?

select v_d_code, v_o_number, v_vin, v_status from vista_details where v_vin
not in (
goole(# select substring(w_vin from '(.{11}$)') from walon);
v_d_code | v_o_number | v_vin | v_status
----------+------------+-------+----------
(0 rows)

--
Gary Stainburn

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Gary Stainburn <gary.stainburn@ringways.co.uk> writes:
> So, who does this select not return the row?

> select v_d_code, v_o_number, v_vin, v_status from vista_details where v_vin
> not in (
> goole(# select substring(w_vin from '(.{11}$)') from walon);

NOT IN with a sub-select that returns any NULL values cannot succeed;
the result is either FALSE (definite match) or NULL (because of the
NULL comparison results).

You could work around that with a COALESCE, but I think a less klugy
and better-performing answer would be to write it as a left join:

select v_d_code, v_o_number, v_vin, v_status from vista_details
left join walon on (v_vin = substring(w_vin from '(.{11}$)'))
where walon.some-never-null-column IS NULL;

The where-clause rejects any actual join matches...

regards, tom lane

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