Re: [SQL] Query runs very slowly in Postgres, but very fast in other DBMS

[Ezequiel Tolnay]

Andrus Moor wrote:
SELECT dokumnr FROM rid WHERE dokumnr NOT IN
(select dokumnr FROM dok);
...
Is it possible to speed up this query is Postgres ? How to force Postgres to 
use indexes for this query ?
Use IN and NOT IN only for small sets. Use JOIN (instead of IN) and LEFT 
JOIN (instead of NOT IN) for larger sets. e.g.:

SELECT rid.dokumnr
FROM rid
LEFT JOIN dok ON (dok.dokumnr = rid.dokumnr)
WHERE dok.dokumnr iS NULL;
Cheers,
Ezequiel Tolnay
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