pingcap/tidb

The update statement reported the truncate error message isn’t compatible with MySQL after column type change

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#24,642 opened on May 13, 2021

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Description

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a char(250) CHARACTER SET utf8);
insert into t set a="";
alter table t modify a char(120) charset binary;
update t set a = 1624877308284165695 where a = 6130350361147116967;

2. What did you expect to see? (Required)

ERROR 1292 (22007): Truncated incorrect DOUBLE value: '0123456789abc\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0'

3. What did you see instead (Required)

ERROR 1292 (22007): Truncated incorrect FLOAT value: ''

4. What is your TiDB version? (Required)

Release Version: v4.0.0-beta.2-2889-gaa3e64d08 Edition: Community Git Commit Hash: aa3e64d08bf19c7230cc3b53c3a57f68a50ae3c3 Git Branch: master

Contributor guide

Tech stack
gosql
Domain
backenddatabase
Issue type
bug
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.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programmingSQL type system understandingTiDB internal error handling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the code path for UPDATE statements that involve column type changes. Look for where truncation errors are generated, likely in the expression evaluation or type conversion modules (e.g., `types/` or `expression/`). The expected error message contains 'DOUBLE value' but actual shows 'FLOAT value', suggesting a mismatch in type inference. Check if the type of the column after ALTER is not being correctly inferred in the UPDATE execution. Files like `executor/executor.go`, `expression/scalar function.go`, or `types/etc.go` may be relevant.
The update statement reported the truncate error message isn’t compatible with MySQL after column type change · pingcap/tidb#24642 | Good First Issue