[CALCITE-1876] Push projections through Aggregate to CsvTableScan

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.15.0
• Component/s: csv-adapter
• Assignee: Julian Hyde
• Reporter: Luis Fernando Kauer
• Created: 07/Jul/17 14:55
• Updated: 09/Dec/17 18:21
• Resolved: 08/Nov/17 19:21

Description

Create a rule to push the projections used in aggregate functions. From Julian Hyde:

Calcite should realize that Aggregate has an implied Project (because it only uses a few columns) and push that projection into the CsvTableScan, but it doesn’t.

A query scans only the used projection when no aggregation is used:

explain plan for select name from emps;

CsvTableScan(table=[[SALES, EMPS]], fields=[[1]])

But it scans all the projections when an aggregation is used:

explain plan for select max(name) from emps;

EnumerableAggregate(group=[{}], EXPR$0=[MAX($1)])
  CsvTableScan(table=[[SALES, EMPS]], fields=[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]])