Bug #117808 Unexpected JSON column DML error with prepare statement

Submitted:	27 Mar 2025 7:21	Modified:	27 Mar 2025 10:00
Reporter:	Xiaocong Ding (OCA)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: Prepared statements	Severity:	S3 (Non-critical)
Version:	8.0.41, 8.4.2	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	JSON ;CHARACTER SET;

Description:
When using a prepared statement to insert/update a JSON column, an unexpected error occurs if the variable type changes between executions. The second execution with a valid JSON string variable fails with ERROR 3144 (22032), even though the session character set is explicitly set to utf8mb4.

How to repeat:
set names utf8mb4;
create table t1 (id int auto_increment primary key, c1 varchar(255), c2 json null);
prepare it from 'insert into t1(c2, c1) values(?, ?)';
set @a=0;
set @b=2;
execute it using @b, @a;
set @b='{}';

# Unexpectedly fails with ERROR 3144
execute it using @b, @a;

Suggested fix:
Each time update/insert a JSON column via a prepare statement, it's necessary to ensure that the Item->m_data_type is correct

Hello Xiaocong Ding,

Thank you for the report and feedback.

regards,
Umesh

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