Samples

The following are left outer join examples.

SELECT * FROM cows_one LEFT OUTER JOIN cows_two ON cows_one.cnumber = 
cows_two.cnumber AND cows_one.cnumber < 3;
cnumber    |  cbreed    |cnumber  | breeds     
-----------|------------|---------+------------
1          | Holstein   |         |            
2          | Guernsey   |2        | Jersey 
3          | Angus      |         |            
(3 rows)
SELECT * FROM cows_one LEFT OUTER JOIN cows_two ON cows_one.cnumber = 
cows_two.cnumber WHERE cows_one.cnumber < 3;
cnumber |  cbreed  |cnumber  | breeds
--------|----------|---------|-------------
2       | Guernsey |2        | Jersey 
1       | Holstein |         |
(2 rows)
SELECT * FROM cows_one LEFT OUTER JOIN cows_two ON cows_one.cnumber = 
cows_two.cnumber AND cows_two.cnumber < 3;
cnumber    |  cbreed    | cnumber | breeds
-----------|------------|---------+------------
1          | Holstein   |         |           
2          | Guernsey   | 2       | Jersey    
3          | Angus      |         |             
(3 rows)
SELECT * FROM cows_one LEFT OUTER JOIN cows_two ON cows_one.cnumber = 
cows_two.cnumber WHERE cows_two.cnumber < 3;
cnumber    |  cbreed    | cnumber | breeds     
-----------|------------|---------+------------
2          | Guernsey   | 2       | Jersey     
(1 row)