showplan output displays “STEP N” for every query, where N is an integer, beginning with “STEP 1”. For some queries, Adaptive Server cannot retrieve the results in a single step and breaks the query plan into several steps. For example, if a query includes a group by clause, Adaptive Server breaks it into at least two steps:
One step to select the qualifying rows from the table and to group them, placing the results in a worktable
Another step to return the rows from the worktable
This example demonstrates a single-step query.
select au_lname, au_fname from authors where city = "Oakland"
QUERY PLAN FOR STATEMENT 1 (at line 1). STEP 1 The type of query is SELECT. FROM TABLE authors Nested iteration. Table Scan. Forward scan. Positioning at start of table. Using I/O Size 2 Kbytes for data pages. With LRU Buffer Replacement Strategy for data pages.
Multiple-step queries are demonstrated following “GROUP BY message”.