sql - How to compare two tables in Postgresql? -

i have 2 identical tables:

a :   id1, id2, qty, unit b:    id1, id2, qty, unit 

the set of (id1,id2) identifying each row , can appear once in each table.

i have 140 rows in table a , 141 rows in table b. find keys (id1,id2) not appearing in both tables. there 1 sure there can't more (for example if each table has whole different data).

i wrote query:

(table except table b) union (table b except table a) ; 

but it's not working. compares whole table don't care if qty or unit different, care id1,id2.

use full outer join:

 select a.*,b.*   full outer join b     on a.id1=b.id1 , a.id2=b.id2 

this show both tables side side. gaps there unmatched row.

 select a.*,b.*   full outer join b     on a.id1=b.id1 , a.id2=b.id2    a.id1 null or b.id1 null; 

that show unmatched rows.

or can use not in

select *    (id1,id2) not in    ( select id1,id2 b ) 

that show rows not matched b.

or same result using join

select a.*    left outer join b    on a.id1=b.id1 , a.id2=b.id2   b.id1 null 

sometimes join faster "not in"