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, 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.