HP 3000 Manuals HP 3000 Manuals
Accessing Mapped Tables IMAGE/SQL provides transparent access to TurboIMAGE/XL data. However, IMAGE/SQL users should keep in mind the considerations described in this section when accessing TurboIMAGE/XL data. Performance Considerations The following factors can affect IMAGE/SQL performance: Up-to-Date Information. 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. [REV BEG] Items in Queries. 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.[REV END] Task 15, "Selecting TurboIMAGE/XL Data with SQL," in Chapter 2 describes these circumstances and gives examples of their use.