JSON_EXTRACT comparisons on cp1251 JSON falsely return ER_OUTOFMEMORY

Comparing a JSON string converted from cp1251 with utf8mb4 literals fails with ER_OUTOFMEMORY, although JSON_UNQUOTE decodes the same value successfully.

This occurs when a JSON_EXTRACT result from a cp1251 JSON string is compared with utf8mb4 text.

Run the control first:

SET NAMES utf8mb4;

SELECT JSON_UNQUOTE(CONVERT('"Ф"' USING cp1251)) = 'Ф' AS control_eq;

It returns:

control_eq

1

Then run each of these statements separately:

SET NAMES utf8mb4;

SELECT JSON_EXTRACT(CONVERT('"Ф"' USING cp1251), '$') = 'Ф' AS candidate_eq;

SET NAMES utf8mb4;

SELECT JSON_EXTRACT(CONVERT('"Ф"' USING cp1251), '$') <=> 'Ф' AS candidate_null_safe_eq;

SET NAMES utf8mb4;

SELECT JSON_EXTRACT(CONVERT('"Ф"' USING cp1251), '$') < 'Х' AS candidate_lt;

Each comparison produces the same error:

ERROR 1037 (HY001): Out of memory; restart server and try again (needed 1 bytes)

The cp1251 JSON character Ф is decoded successfully by the control. The ordinary equality and null-safe equality comparisons should therefore return 1, and the ordering comparison Ф < Х should also return 1, without an allocation error.