analyzing intermediate query

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I noticed that query

SELECT dok.*
FROM dok
JOIN  (SELECT DISTINCT dokumnr FROM  temptbl ) x USING(dokumnr);

is slow in 8.1.4
I cannot use explain analyze since this query uses results from temporary table temptbl which is not available.

Sometimes innter table returns only 1 row so maybe seq scan is selected instead of single row index access becauses expected count is 1000

As I understand, PostgreSql requires manually running ANALYZE for temporary tables if their row count is different from 1000

How to force PostgreSql to analyze inner table in this query or use other way to get index using query plan if inner query returns single row ?

How

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