An execution plan is the set of steps the database server uses to access information in the database related to a statement. The execution plan for a statement can be saved and reviewed, regardless of whether it was just optimized, whether it bypassed the optimizer, or whether its plan was cached from previous executions. A query execution plan may not correspond exactly to the syntax used in the original statement, and may use materialized views instead of the base tables explicitly specified in the query. However, the operations described in the execution plan are semantically equivalent to the original query.

You can view the execution plan in Interactive SQL or using SQL functions. You can choose to retrieve the execution plan in several different formats:

• Short text plan
• Long text plan
• Graphical plan
• Graphical plan with root statistics
• Graphical plan with full statistics
• UltraLite (short, long, or graphical)

You can also obtain plans for SQL queries with a particular cursor type by using the GRAPHICAL_PLAN and EXPLANATION functions. See GRAPHICAL_PLAN function [Miscellaneous], and EXPLANATION function [Miscellaneous].

Additional reading

For more information about phases a statement goes through until it is executed, see Phases of query processing.

For more information about the rules that the database server follows when rewriting your query, see:

• Semantic query transformations
• Rewriting subqueries as EXISTS predicates
• Improving performance with materialized views

For information about the algorithms and methods that the optimizer uses to implement your query, see Query execution algorithms.

For more information about how to access a graphical plan, see Viewing graphical plans.

For information about how to read execution plans, see Reading text plans, and Reading graphical plans.