update - which way quicker? - Mailing list pgsql-performance

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!