Difference between left join and left outer join

Question

Difference between left join and left outer join

Answer 1

Description

LEFT JOIN or LEFT OUTER JOIN

The result set of a left outer join includes all the rows from the left table specified in the LEFT OUTER clause, not just the ones in which the joined columns match. When a row in the left table has no matching rows in the right table, the associated result set row contains null values for all select list columns coming from the right table.

Reference:

As per the documentation: [FROM (Transact-SQL)](http://msdn.microsoft.com/en-us/library/ms177634(SQL.90%29.aspx):

<join_type> ::=
    [ { INNER | { { LEFT | RIGHT | FULL } [ OUTER ] } } [ <join_hint> ] ]
    JOIN

The keyword OUTER is marked as optional (enclosed in square brackets), and what this means in this case is that whether you specify it or not makes no difference. Note that while the other elements of the join clause is also marked as optional, leaving them out will of course make a difference.

For instance, the entire type-part of the JOIN clause is optional, in which case the default is INNER if you just specify JOIN. In other words, this is legal:

SELECT * FROM A JOIN B ON A.X = B.Y

Here's a list of equivalent syntaxes:

A LEFT JOIN B            A LEFT OUTER JOIN B
A RIGHT JOIN B           A RIGHT OUTER JOIN B
A FULL JOIN B            A FULL OUTER JOIN B
A INNER JOIN B           A JOIN B

Thank you.