For better performance, it is important to have
accurate statistics on the tables.
Use the SQL UPDATE STATISTICS statement to ensure that this
information is up-to-date. Mapped table statistics should
be updated immediately after
the database is attached and again when the number of data entries in mapped
tables has changed significantly.
Refer to the ALLBASE/SQL Database Administration Guide for information about how to use this statement.
When a mapped column represents a TurboIMAGE/XL key item, search item, or the item which has a third-party index or an explicit or implicit B-Tree index, IMAGE/SQL uses this item
to retrieve the data more efficiently whenever possible. (An explicit B-Tree index is on a master's key item, while an implicit B-Tree index is on a detail's search item whose related key item of the master has a B-Tree index.)
Because of this, using such a mapped column in the WHERE clause of an SQL SELECT statement
can improve performance in certain circumstances.
Task 15, "Selecting TurboIMAGE/XL Data with SQL," in Chapter 2
describes these circumstances and gives
examples of their use.
