[TAJO-1010] Improve multiple DISTINCT aggregation.

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.9.0
• Component/s: Planner/Optimizer
• Assignee: JaeHwa Jung
• Reporter: JaeHwa Jung
• Created: 18/Aug/14 09:52
• Updated: 20/Nov/14 12:18
• Resolved: 08/Oct/14 02:38

Description

Currently, tajo provides three stage for optimizing distinct query aggregation. But it just supports one column for distinct aggregation as follows:

Query1

select a.flag, count(distinct a.id) as cnt, sum(distinct a.id) as total
from table1
group by a.flag

If you write two more columns for distinct aggregation, you can't apply optimized distinct aggregation as follows:

Query2

select a.flag, count(distinct a.id) as cnt, sum(distinct a.id) as total
, count(distinct a.name) as cnt2, count(distinct a.code) as cnt3
from table1
group by a.flag

In this case, you may see low performance for your query. Thus, we need to improve multiple DISTINCT aggregation. Correctly, we should support three stage for multiple DISTINCT aggregation.

Issue Links

• is related to: TAJO-601 Improve distinct aggregation query processing