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

try this query :

SELECT rid.dokumnr as d1 ,dok.dokumnr as d2  FROM rid left join dok on 
rid.dokumnr = dok.dokumnr where dok.dokumnr is null;


> Tables:
>
> CREATE TABLE dok ( dokumnr NUMERIC(12),
>             CONSTRAINT dok_pkey PRIMARY KEY (dokumnr) );
> CREATE TABLE rid ( dokumnr NUMERIC(12) );
> CREATE INDEX rid_dokumnr_idx ON rid (dokumnr);
>
> Query:
>
> SELECT dokumnr FROM rid WHERE dokumnr NOT IN
> (select dokumnr FROM dok);
>
> runs VERY slowly in Postgres. It uses the following query plan:
>
> Seq Scan on rid  (cost=0.00..28698461.07 rows=32201 width=14)
>   Filter: (NOT (subplan))
>   SubPlan
>     ->  Seq Scan on dok  (cost=0.00..864.29 rows=10729 width=14)
>
> In Microsoft Visual FoxPro this query runs fast. FoxPro uses indexes speed
> up the query by comparing bitmaps.
>
> Is it possible to speed up this query is Postgres ? How to force Postgres
> to use indexes for this query ?
>
> Andrus
>
>
>
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