IS NULL vs IS NOT NULL

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От Vig, Sandor (G/FI-2)
Тема IS NULL vs IS NOT NULL
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Msg-id 977921B17B2F2048AA5AAE9B4CBB713E01423D42@huaudigs0035.audi.de
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Ответы Re: IS NULL vs IS NOT NULL  (Stephan Szabo <sszabo@megazone.bigpanda.com>)
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Hi,

Another "funny" thing: I have a query which runs
on (Linux) PostgreSQL 7.4.x under 10 sec. I tried
to run it on (Windows) PostgreSQL 8.0 yesterday.
It didn't finished at all! (I shoot it down after 10 minutes)
I made various tests and I figured out something interesting:
The same query with:
    A, "history.undo_action_id > 0" runs in 10 sec.
    B, "history.undo_action_id is not null" runs in 10 sec.
    C, "history.undo_action_id is null" runs forever (?!)
I used EXPLAIN but I couldn't figure out what the problem was.
In every explain output are 3 lines:
"                    ->  Index Scan using speed_3 on history  (.........)"
"                          Index Cond: (type_id = 6)"
"                          Filter: (undo_action_id IS NOT NULL)"
where "speed_3" is a btree index on history.type_id. There is also an index
for history.undo_action_id (btree) but it is not used.

The tables are well indexed, and have about 200.000 records.

The SQL file and the 3 scenarios are in attachment.

Help, anyone?

Vig Sándor

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