PostgreSQL Development Essentials

Using the Outer join

Another class of join is known as the OUTER JOIN. In OUTER JOIN, the results might contain both matched and unmatched rows. It is for this reason that beginners might find such joins a little confusing. However, the logic is really quite straightforward.

The following are the three types of Outer joins:

• The PostgreSQL LEFT OUTER JOIN (or sometimes called LEFT JOIN)
• The PostgreSQL RIGHT OUTER JOIN (or sometimes called RIGHT JOIN)
• The PostgreSQL FULL OUTER JOIN (or sometimes called FULL JOIN)

Left outer join

Left outer join returns all rows from the left-hand table specified in the ON condition, and only those rows from the other tables where the joined fields are equal (the join condition is met). If the condition is not met, the ...