Modifying Access Paths › Modifying Access Path Details › SQL and DDS Joins

SQL and DDS Joins

To join information from tables/files, SQL uses inner joins and DDS uses outer joins. Outer joins are not part of the American National Standards Institute (ANSI) standard for SQL. If you switch an access path from DDS to SQL or vice versa, be aware that the same records might not be included.

The following examples illustrate an SQL inner join and a DDS outer join, where the joins resolve to a different set of records:

In the preceding example, the customer record for Order # 002, Cust. # 2, does not exist in the Customer file. In the SQL join file, the record for Order # 002 is dropped from the file. In the DDS join file, the record for Order # 002 is included in the file. Note that the virtual field Cust. Name is filled with blanks in the DDS join file.