The SQLite grammar is a bit different from the SQL-92 spec’s, according to which, the following are illegal:
*OUTER JOIN
*NATURAL OUTER JOIN
*NATURAL CROSS JOIN
The first two, because a <join type>, in order to contain OUTER, must also include an <outer join type> before it. The last, because NATURAL can only occur in <qualified join>‘s, not <cross join>‘s. These don’t appear to behave according to any spec, so it’s a good idea to avoid them.
As was answered on the mailing list, SQLite3 only supports three joins: CROSS JOIN, INNER JOIN, and LEFT OUTER JOIN. The following are equivalent:
, == CROSS JOIN
JOIN == INNER JOIN
LEFT JOIN == LEFT OUTER JOIN
As explained in the wikipedia article the NATURAL keyword is shorthand for finding and matching on same-name columns, and doesn’t affect the the join type.
According to the SQLite page, ‘RIGHT‘ and ‘FULL‘ OUTER JOIN‘s are not supported.