When you plan to join data sources (tables or subqueries),
the order in which you add the data sources to the workspace matters.
The first data source that is added to the workspace is automatically
assigned as the left table for any joins that you add to the data
query.
If you are creating
a data query that uses a fact table and dimension tables, it is simplest
to drag and drop the fact table onto the workspace first. You can
perform left, right, or full joins with the dimension tables faster
because you need to specify the join type only. However, if you drag
and drop a dimension table first, you can easily use the
button on the
Joins tab
to switch the left and right tables in the join.
If you are not using
a fact table or dimension tables, then the sequence for adding tables
to the workspace might not be very important. Just remember that the
first table dropped onto the workspace is assigned as the left table,
and you can switch the left table and right table on the
Joins tab. The data builder takes advantage
of vendor-specific features in SQL processing whenever possible. If
the source tables are from a third-party vendor database, the
SAS/ACCESS
Interface engine can optimize the performance of the data query by
passing the SQL statements through to the database.