Join/inner join

An inner join, also known as a simple join, returns rows from joined tables that have matching rows. It does not include rows from either table that have no matching rows in the other.

SELECT * FROM cows_one INNER JOIN cows_two ON cows_one.cnumber = 
cows_two.cnumber;
cnumber     | cbreed     | cnumber  | breeds
------------+------------+----------+---------
2           | Guernsey   | 2        | Jersey
3           | Angus      | 3        | Brown Swiss
(2 rows)

The keyword inner is optional.