pingcap/tidb

Support not null ScalarFunction.

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#9,965 opened on Mar 31, 2019

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help wanted

Description

Feature Request

Describe the feature you'd like:

Currently, TiDB Don't have not null ScalarFunction, the implementation of not null is not (is null).

Separate implementation of not null must be better than the composed of two 2 ScalarFunction.

Next step: implement not null in TiKV coprocessor and push down.

Contributor guide

Tech stack
go
Domain
databasebackend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Go programmingTiDB expression frameworkTiKV coprocessor basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Examine how existing scalar functions like `is null` and `not` are implemented in TiDB's expression package (e.g., `expression/scalar function.go`). Design a new `not null` scalar function that performs the inverse of `is null`. Then implement the function and ensure it supports coprocessor pushdown to TiKV. Review the TiKV coprocessor code for adding new scalar functions, following the pattern of existing implementations.