Обсуждение: update - which way quicker?

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!

On 2008-08-28, at 21:31, Emi Lu wrote:

> 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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Check EXISTS

http://www.postgresql.org/docs/8.3/interactive/functions-subquery.html


Serdecznie pozdrawiam

Pawel Socha
pawel.socha@gmail.com

programista/administrator

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