The type of query is SELECT (into WorktableN).
Queries using a group by clause first put qualifying results into a worktable. The data is grouped as the table is generated. A second step returns the grouped rows.
The following example returns a list of all cities and indicates the number of authors that live in each city. The query plan shows the two steps: the first step selects the rows into a worktable, and the second step retrieves the grouped rows from the worktable:
select city, total_authors = count(*)
from authors
group by city
QUERY PLAN FOR STATEMENT 1 (at line 1).
STEP 1
The type of query is SELECT (into Worktable1).
GROUP BY
Evaluate Grouped COUNT AGGREGATE.
FROM TABLE
authors
Nested iteration.
Table Scan.
Forward scan.
Positioning at start of table.
Using I/O Size 16 Kbytes for data pages.
With LRU Buffer Replacement Strategy for data pages.
TO TABLE
Worktable1.
STEP 2
The type of query is SELECT.
FROM TABLE
Worktable1.
Nested iteration.
Table Scan.
Forward scan.
Positioning at start of table.
Using I/O Size 16 Kbytes for data pages.
With MRU Buffer Replacement Strategy for data pages.
