The query plan is the steps the Adaptive Server optimizer follows as it executes a SQL statement. Each line represents how the Adaptive Server optimizer will physically retrieve rows of data from the database or how the data is prepared. The Adaptive Server optimizer performs the child step before the parent step. Depending on the SQL statement, the parent step may be executed when a single row has been returned from the child step. Some query plans may require all rows to be returned from the child step before executing the parent step.
By examining the query plan, you can see exactly how the database executes your SQL statement, helping you judge whether the SQL statement is the most efficient.
You can use the Query Plan page of the SQL Information pane to view the steps Adaptive Server follows to execute the SQL statement. You can animate the plan to show you the progression of the plan steps. You can look up the explanation of the query plan operations.