Edit

Recordset: Performing a Join (ODBC)

  • Article

This topic applies to the MFC ODBC classes.

What a Join Is

The join operation, a common data-access task, lets you work with data from more than one table using a single recordset object. Joining two or more tables yields a recordset that can contain columns from each table, but appears as a single table to your application. Sometimes the join uses all columns from all tables, but sometimes the SQL SELECT clause in a join uses only some of the columns from each table. The database classes support read-only joins but not updateable joins.

To select records containing columns from joined tables, you need the following items:

  • A table list containing the names of all tables being joined.

  • A column list containing the names of all participating columns. Columns with the same name but from different tables are qualified by the table name.

  • A filter (SQL WHERE clause) that specifies the columns on which the tables are joined. This filter takes the form "Table1.KeyCol = Table2.KeyCol" and actually accomplishes the join.

You can join more than two tables in the same way by equating multiple pairs of columns, each pair joined by the SQL keyword AND.

See also

Recordset (ODBC)
Recordset: Declaring a Class for a Predefined Query (ODBC)
Recordset: Declaring a Class for a Table (ODBC)
Recordset: Requerying a Recordset (ODBC)