update - which way quicker?

From: Emi Lu <emilu(at)encs(dot)concordia(dot)ca>
To: pgsql-performance(at)postgresql(dot)org
Subject: update - which way quicker?
Date: 2008-08-28 19:31:04
Message-ID: 48B6FCF8.3090807@encs.concordia.ca
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Good morning,

Tried to compare Table1 based on Table2

. update table1.col = false
if table1.pk_cols not in table2.pk_cols

For the following two ways, (2) always performs better than (1) right,
and I need your inputs.
========================================================================
(1) update table1
set col = false
where table1.pk_co1 || table1.pk_col2.... || table1.pk_colN

NOT IN

(select pk_co1 || pk_col2.... || pk_colN
from table2
)

(2) ResultSet(rs) =
select pk_col1||pk_col2... || pk_colN
from table1
left join table2 using (pk_col1..., pk_colN)
where table2.pk_col1 is null

Then for each rs record, do:
update table1
set col = false
where col1||... colN in rs.value

Thanks a lot!

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