This node represents the grouping of rows.
Node name: GRPBY
Represents: The
grouping of rows according to common values of designated columns
or functions. This operation is required to produce a group of values,
or to evaluate set functions.
If no GROUP BY columns are specified,
the GRPBY node can still be used if there are aggregation functions
in the SELECT list, indicating that the entire table is treated as
a single group when doing that aggregation.
Performance
suggestions: - This node represents a necessary operation. To improve access plan costs,
concentrate on other nodes (such as scans and joins) that define the
set of rows to be grouped.
- To improve the performance
of a SELECT statement that contains a single aggregate function but
no GROUP BY clause, try the following:
- For a MIN(C) aggregate
function, create an ascending index on
C.
- For a MAX(C) aggregate function, create a descending index
on
C.