MariaDB 10.5

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show variables like '%char%';

Variable_name
Value

character_set_client
utf8mb4

character_set_connection
utf8mb4

character_set_database
utf8mb4

character_set_filesystem
binary

character_set_results
utf8mb4

character_set_server
utf8mb4

character_set_system
utf8

character_sets_dir
/usr/share/mysql/charsets/

SELECT VERSION();

VERSION()

10.5.17-MariaDB-1:10.5.17+maria~deb11

-- --------------------------------------------------------
-- Host:                         127.0.0.1
-- Server version:               10.5.4-MariaDB - mariadb.org binary distribution
-- Server OS:                    Win64
-- HeidiSQL Version:             11.0.0.6099
-- --------------------------------------------------------

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET NAMES utf8 */;
/*!50503 SET NAMES utf8mb4 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;

-- Dumping structure for table test.utferror
CREATE TABLE IF NOT EXISTS `utferror` (
  `txtField` varchar(8) COLLATE utf8mb4_unicode_ci NOT NULL,
  `bitField` bit(1) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

-- Dumping data for table test.utferror: ~0 rows (approximately)
/*!40000 ALTER TABLE `utferror` DISABLE KEYS */;
INSERT INTO `utferror` (`txtField`, `bitField`) VALUES
	('abc😁', b'0'),
	('😁def', b'1');
/*!40000 ALTER TABLE `utferror` ENABLE KEYS */;

/*!40101 SET SQL_MODE=IFNULL(@OLD_SQL_MODE, '') */;
/*!40014 SET FOREIGN_KEY_CHECKS=IF(@OLD_FOREIGN_KEY_CHECKS IS NULL, 1, @OLD_FOREIGN_KEY_CHECKS) */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;

Records: 2  Duplicates: 0  Warnings: 0

SELECT JSON_ARRAYAGG(JSON_ARRAY(txtField)) FROM `utferror`; -- works fine

JSON_ARRAYAGG(JSON_ARRAY(txtField))

[["abc😁"],["😁def"]]

SELECT JSON_ARRAYAGG(JSON_ARRAY(txtField, bitField)) FROM `utferror`; -- enconding error

JSON_ARRAYAGG(JSON_ARRAY(txtField, bitField))

[["abc\uD83DDE01", ,["\uD83DDE01def", ]

SELECT JSON_ARRAYAGG(JSON_ARRAY(txtField, CONVERT(bitField USING UTF8MB4))) FROM `utferror`; -- works

JSON_ARRAYAGG(JSON_ARRAY(txtField, CONVERT(bitField USING UTF8MB4)))

[["abc😁", "\u0000"],["😁def", "\u0001"]]

Variable_name	Value
character_set_client	utf8mb4
character_set_connection	utf8mb4
character_set_database	utf8mb4
character_set_filesystem	binary
character_set_results	utf8mb4
character_set_server	utf8mb4
character_set_system	utf8
character_sets_dir	/usr/share/mysql/charsets/