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create table t1 ( id serial primary key, n numeric not null , s varchar(300) ); create table t2 ( id serial primary key, n numeric not null , s varchar(300) ); create table log (ts timestamp); insert into t1(n,s) select 1 , rpad('x',300,'x') from generate_series(1,1000000); insert into t2(n,s) select 1 , rpad('x',300,'x') from generate_series(1,1000000); --------- insert into log values (current_timestamp); -- \timing on -- explain (analyze, timing false) update t1 set n = 2 where id >= 990000; insert into log values (current_timestamp); do $$ declare i record; begin for i in (select id from t2 where id >= 990000) loop update t2 set n = 3 where id = i.id; end loop; end; $$ language plpgsql; insert into log values (current_timestamp); -------- select *, ts - lag(ts) over(order by ts) from log;