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SQL Anywhere 12.0.0 (Français) » SQL Anywhere Server - SQL Usage » Query optimization and execution » Query execution algorithms » Table access methods

 

MultipleIndexScan method (MultIdx)

MultipleIndexScan is used when more than one index can or must be used to satisfy a query that contains a set of search conditions that are combined with the logical operators AND or OR. MultipleIndexScan combines multiple IndexScan methods with other operators to satisfy the search conditions.

When multiple indexes are used to evaluate predicates combined using an AND operator, MultipleIndexScan performs an index intersection operation. When used to evaluate predicates combined using an OR operator, MultipleIndexScan performs an index union operation. However, note that MultipleIndexScan is not restricted to the union or intersection operations; for example, MultipleIndexScan may perform and index union by using outer joins.

You can determine whether a multiple index scan is used for a particular query by examining the execution plan. In a short plan, a multiple index scan method appears as table-name<MultIdx..., followed by a list of the indexes that were used.

In long and graphical plans, the use of a multiple index scan is indicated by a MultipleIndexScan node, where the entries under the node provide details about which indexes were used, and how their results were combined.

 See also