The flen of conv function should be 65

Description

SELECT CONV(123, 10, 10);

Field   1:  `CONV(123, 10, 10)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       VAR_STRING
Collation:  utf8mb4_0900_ai_ci (255)
Length:     260
Max_length: 3
Decimals:   31
Flags:


+-------------------+
| CONV(123, 10, 10) |
+-------------------+
| 123               |
+-------------------+
1 row in set (0.00 sec)

mysql> SELECT CONV(123, 10, 10);
Field   1:  `CONV(123, 10, 10)`
Catalog:    `def`
Database:   ``
Table:      ``
Org_table:  ``
Type:       VAR_STRING
Collation:  utf8mb4_bin (46)
Length:     256
Max_length: 3
Decimals:   31
Flags:      NOT_NULL


+-------------------+
| CONV(123, 10, 10) |
+-------------------+
| 123               |
+-------------------+
1 row in set (0.00 sec)

Contributor guide

Tech stack

gosql

Domain

database

Issue type

bug

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

2

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

under 1 hour

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

fresh

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

Go programmingTiDB codebase structureSQL function implementation

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

40

Research direction

Look at the implementation of the CONV function in TiDB, likely in the expression package (e.g., `expression/builtin string.go` or similar). The flen is currently set to 256 but should be 260 to match MySQL. Search for where `flen` is assigned for CONV and change it to 65? Wait, the title says flen should be 65, but the body compares 256 vs 260. This inconsistency needs clarification. Maybe the issue is that the flen for the CONV result should be 65 * 4 = 260? Actually, the expected Length is 260, which is 65*4 (since utf8mb4 uses 4 bytes per character). So the flen in number of characters should be 65. Check the MySQL source or TiDB's handling of CONV length. The fix is likely a one line change of a constant.