In the query rewrite involving aggregates, add the columns for aggregation.

See Also

addNewColumnsForAggregation

Add the extra result columns required by the aggregates to the result list.

Exceptions

StandardException:

standard exception policy

Add any distinct aggregates to the order by list. Asserts that there are 0 or more distincts.

Add a whole slew of columns needed for aggregation. Basically, for each aggregate we add 3 columns: the aggregate input expression and the aggregator column and a column where the aggregate result is stored. The input expression is taken directly from the aggregator node. The aggregator is the run time aggregator. We add it to the RC list as a new object coming into the sort node.

At this point this is invoked, we have the following tree:

PR - (PARENT): RCL is the original select list | PR - GROUP BY: RCL is empty | PR - FROM TABLE: RCL is empty

For each ColumnReference in PR RCL

• clone the ref
• create a new RC in the bottom RCL and set it to the col ref
• create a new RC in the GROUPBY RCL and set it to point to the bottom RC
• reset the top PR ref to point to the new GROUPBY RC

• create RC in FROM TABLE. Fill it with aggs Operator.
• create RC in FROM TABLE for agg result
• create RC in FROM TABLE for aggregator
• create RC in GROUPBY for agg input, set it to point to FROM TABLE RC
• create RC in GROUPBY for agg result
• create RC in GROUPBY for aggregator
• replace Agg with reference to RC for agg result

For a query like,

	  select c1, sum(c2), max(c3)
	  from t1 
	  group by c1;
	  

	    ProjectRestrictNode RCL -> (ptr to GBN(column[0]), ptr to GBN(column[1]), ptr to GBN(column[4]))
	              |
	    GroupByNode RCL->(C1, SUM(C2), <agg-input>, , MAX(C3), <agg-input>, <aggregator>)
	              |
	    ProjectRestrict RCL->(C1, C2, C3)
	              |
	    FromBaseTable
	    

The Aggregator function puts the results in the first of the 3 RC's and the PR resultset in turn picks up the value from there.

The notation (ptr to GBN(column[0])) basically means that it is a pointer to the 0th RC in the RCL of the GroupByNode.

The addition of these unagg and agg columns to the GroupByNode and to the PRN is performed in addUnAggColumns and addAggregateColumns.

Note that that addition of the GroupByNode is done after the query is optimized (in SelectNode#modifyAccessPaths) which means a fair amount of patching up is needed to account for generated group by columns.

Exceptions

StandardException:

standard exception policy

Add a new PR node for aggregation. Put the new PR under the sort.

Exceptions

StandardException:

standard exception policy

In the query rewrite for group by, add the columns on which we are doing the group by.

Returns:ArrayList<SubstituteExpressionVisitor>

havingRefsToSubstitute visitors array. Return any havingRefsToSubstitute visitors since it is too early to apply them yet; we need the AggregateNodes unmodified until after we add the new columns for aggregation (DERBY-4071).

See Also

addNewColumnsForAggregation

Generate the code to evaluate grouped aggregates.

Generate the code to evaluate scalar aggregates.

Method for creating a new result column referencing the one passed in.

Parameters

targetRC:ResultColumn

the source

Returns:ResultColumn

the new result column

Exceptions

StandardException:

on error