Books online explaisn as follows:
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.
Summary:
LEFT OUTER JOIN - brings all records from the left table
LEFT JOIN - Brings only the records that match from the left.
The RIGHT JOIN and the similar LEFT JOIN operations can be used in any FROM clause to combine records from two tables. The LEFT JOIN operation is used to create a left outer join and includes all of the records from the first (left) of the two tables, even if there are no matching values for records in the second. The RIGHT JOIN operation is used to create a right outer join and includes all of the records from the second (right) of the two tables, even if there are no matching values for records in the first.
I just tried LEFT JOIN and LEFT OUTER JOIN on a query involving two tables that have a common field upon which I made the join. The LEFT table had two records that had no match in the other table. When I ran LEFT OUTER JOIN and when I ran LEFT JOIN I got 1243 records both ways.
If I want just the matching records I use and INNER JOIN.
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