Re: please help on query

On Thu, 2002-07-11 at 17:22, Luis Alberto Amigo Navarro wrote:
> I can't improve performance on this query:

You could try rewriting the IN's into = joins
or even use explicit INNER JOIN syntax to force certain plans

with a select inside another and depending on value of partsupp.partkey
it is really hard for optimiser to do anything else than to perform the
query for each row.

But it may help to rewrite

SELECT
partsupp.suppkey
FROM
partsupp
WHERE
partsupp.partkey IN (
SELECT
part.partkey
FROM
part
WHERE
part.name like 'forest%'
)
AND partsupp.availqty>(
SELECT
0.5*(sum(lineitem.quantity)::FLOAT)
FROM
lineitem
WHERE
lineitem.partkey=partsupp.partkey
AND lineitem.suppkey=partsupp.partkey
AND lineitem.shipdate>=('1994-01-01')::DATE
AND lineitem.shipdate<(('1994-01-01')::DATE+('1
year')::INTERVAL)::DATE
)
)

into

SELECT
partsupp.suppkey
FROM
partsupp,
(SELECT part.partkey as partkey
FROM part
WHERE part.name like 'forest%'
) fp,
(SELECT 0.5*(sum(lineitem.quantity)::FLOAT) as halfsum,
partkey
FROM lineitem
WHERE
lineitem.partkey=partsupp.partkey
AND lineitem.suppkey=partsupp.partkey
AND lineitem.shipdate>=('1994-01-01')::DATE
AND lineitem.shipdate<(('1994-01-01')::DATE+('1
year')::INTERVAL)::DATE
) li
WHERE partsupp.partkey = fp.partkey
AND partsupp.partkey = li.partkey
AND partsupp.availqty > halfsum

if "lineitem" is significantly smaller than "partsupp"

But you really should tell us more, like how many lines does lineitem
and other tables have,

----------
Hannu