The SPD Server's enhanced
SQL planner includes the STARJOIN facility. The SPD Server STARJOIN
facility validates, optimizes, and executes SQL queries on data that
is configured in a star schema. Star schemas consist of two or more
normalized dimension tables that surround a centralized fact table.
The centralized fact table contains data elements of interest derived
from the dimension tables.
In data warehouses with
large numbers of tables and millions or billions of rows of data,
properly constructed star joins can minimize overhead data redundancy
during query evaluation. If the SPD Server STARJOIN facility is not
enabled, or of SPD Server SQL does not detect a star schema, then
the SQL is processed using pair-wise joins.
How do star joins differ
from pair-wise joins? In SPD Server 4.4, properly configured star
joins require only three steps to complete, regardless of the number
of dimension tables. SPD Server pair-wise joins require one step for
each table to complete the join. If a star schema consisted of 25
dimension tables and one fact table, the STARJOIN is accomplished
in three steps; joining the tables in the star schema using pair-wise
joins requires 26 steps.
When data is configured
in a valid SPD Server star schema, and the STARJOIN facility is not
disabled, the SPD Server STARJOIN facility can produce quicker and
more processor-efficient SQL query performance than would be realized
using SQL pair-wise join queries.