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, then the simplest approach is 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 must specify only the
join type. However, if you drag and drop a
dimension table first, then 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, then the
SAS/ACCESS Interface
engine can optimize the performance of the data query by passing the SQL statements through
to the database.