Processing Queries

This section describes various options for processing a SELECT statement, or query, that involves a virtual index. An SQL query requests that the database server fetch and assemble stored data into rows. A SELECT statement often includes a WHERE clause that specifies the values that a row must have to qualify for selection.

Query processing involves the following actions:

• Interpreting the scan and qualification descriptors
• Scanning the index to select index entries
• Optionally returning rows that satisfy the query
• Maintaining cost and distribution information for the optimizer