In Adaptive Server, there are two kinds of query plans:
Legacy query plans from versions earlier than 15.0 are still used for SQL statements that are not executed by the query engine, such as set or create table, and so on.
In version 15.0 and later, the query plans chosen by the optimizer are executed by the query execution engine.
The legacy query plans are unchanged in Adaptive Server 15.0, and their showplan output is also unchanged.
The query plans that are executed by the query engine are different from those executed by the query engine in versions of Adaptive Server earlier than 15.0. The corresponding showplan output has changed significantly as well. Some of the new features of the query plans that showplan must display include:
Plan elements – query plans can be composed from over thirty different operators.
Plan shape – query plans are upside down trees of operators. In general, more operators in a query plan results in more combinations of possible tree shapes.15.0 query plans can be more complex than those found in earlier Adaptive Server Enterprise versions. Nested indentation is provided to assist in visualizing the tree shape of these query plans.
Subplans that are executed in parallel.
The rest of this chapter describes the showplan output for query plans.
