pingcap/tidb

push avg & distinct functions across join when tidb_opt_agg_push_down is set

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#16,355 opened on Apr 14, 2020

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Description

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

When tidb_opt_agg_push_down is on, currently it does not support pushing avg function and distinct functions across Join.

After https://github.com/pingcap/tidb/pull/16344, it supports pushing those across Union, we should make it happen w/ Join, too.

2. What did you expect to see?

3. What did you see instead?

4. What version of TiDB are you using? (tidb-server -V or run select tidb_version(); on TiDB)

e90aac271

Contributor guide

Research direction
Inspect the implementation of aggregate pushdown for Union in PR #16344 and apply similar logic to Join operators. Focus on how avg and distinct aggregates are handled during pushdown across Join.
Tech stack
go
Domain
backenddatabase
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GoTiDB query optimization concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50