Pre-sorting can be the most effective means to improve
overall join performance. A table that participates in multiple joins
on the same join key usually benefits from pre-sorting. For example,
if the ACCOUNT table participates in four joins on ACCOUNT_ID, then
pre-sorting the ACCOUNT table on ACCOUNT_ID helps optimize three joins.
However, the overhead that is associated with sorting can degrade
performance. You can sometimes achieve better performance when you
subset by using the list of columns in the SELECT statement and the
conditions set in the WHERE clause.
Note: Integrity constraints
are automatically generated when the query target to the SQL transformation
is a physical table. You can control the generation of these constraints
by using a Table Loader transformation between the SQL Join transformation
and its physical table.