MDAC 2.5 SDK - ODBC Programmer's Reference
Chapter 8: SQL Statements

Outer Joins

ODBC supports the SQL-92 left, right, and full outer join syntax. The escape sequence for outer joins is

{oj outer-join}

where outer-join is

table-reference {LEFT | RIGHT | FULL} OUTER JOIN
     {table-reference | outer-join} ON search-condition

table-reference specifies a table name, and search-condition specifies the join condition between the table-references.

An outer join request must appear after the FROM keyword and before the WHERE clause (if one exists). For complete syntax information, see "Outer Join Escape Sequence" in Appendix C, "SQL Grammar."

For example, the following SQL statements create the same result set that lists all customers and shows which has open orders. The first statement uses the escape-sequence syntax. The second statement uses the native syntax for Oracle and is not interoperable.

SELECT Customers.CustID, Customers.Name, Orders.OrderID, Orders.Status
   FROM {oj Customers LEFT OUTER JOIN Orders ON Customers.CustID=Orders.CustID}
   WHERE Orders.Status='OPEN'

SELECT Customers.CustID, Customers.Name, Orders.OrderID, Orders.Status
   FROM Customers, Orders
   WHERE (Orders.Status='OPEN') AND (Customers.CustID= Orders.CustID(+))

To determine the types of outer joins that a data source and driver support, an application calls SQLGetInfo with the SQL_OJ_CAPABILITIES flag. The types of outer joins that might be supported are left, right, full, or nested outer joins; outer joins in which the column names in the ON clause do not have the same order as their respective table names in the OUTER JOIN clause; inner joins in conjunction with outer joins; and outer joins using any ODBC comparison operator. If the SQL_OJ_CAPABILITIES information type returns 0, no outer join clause is supported.