||SQL Server Tips by Gama and Naughter
An outer left join returns not only the rows that meet the join
conditions but also all the rows from the table on the left of the
JOIN clause, even if they have no correspondent column from the
table on the right. If there is no correspondence on the right table
a NULL value(s) will be assigned.
Example: To display all publishers, even the ones with no titles in
the title database. When the publisher has no title in the database,
the returned title will be NULL.
FROM dbo.publishers LEFT OUTER JOIN
dbo.titles ON dbo.publishers.pub_id = dbo.titles.pub_id
The above book excerpt is from:
Turbocharge Database Performance with C++ External Procedures
Joseph Gama, P. J. Naughter