Gavin 'Beau' Baumanis wrote:
>
> The copy is inside the same table, so I don't understand why it (the
> required query ) would require any joins.
Maybe you should use FROM clause in the update that references a
row-valued subquery?
craig=# create table x ( id serial, val integer );
NOTICE: CREATE TABLE will create implicit sequence "x_id_seq" for
serial column "x.id"
CREATE TABLE
craig=# insert into x ( val ) values ( 4 ) , ( 6 ) ;
INSERT 0 2
craig=# select * from x;id | val
----+----- 1 | 4 2 | 6
(2 rows)
craig=# update x set val = foundrow.val from ( select val from x where
id = 2 ) as foundrow where id = 1 ;
UPDATE 1
craig=# select * from x;id | val
----+----- 2 | 6 1 | 6
(2 rows)
craig=# insert into x ( val ) select generate_series(0,10000);
INSERT 0 10001
craig=# explain update x set val = foundrow.val from ( select val from x
where id = 4123 ) as foundrow where id = 5912 ; QUERY PLAN
-------------------------------------------------------------------------Nested Loop (cost=0.00..16.55 rows=1
width=14) -> Index Scan using x_id_idx on x (cost=0.00..8.27 rows=1 width=10) Index Cond: (id = 5912) ->
IndexScan using x_id_idx on x (cost=0.00..8.27 rows=1 width=4) Index Cond: (public.x.id = 4123)
(5 rows)
Will that do the job?
--
Craig Ringer
