Detailed explanation of the use of MySQL comparison operator regular expression matching REGEXP

DROP TABLE IF EXISTS `test_01`;
CREATE TABLE `test_01` (
 `id` int(0) NOT NULL,
 `stu` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT 'Student number',
 `user` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT 'User',
 `km` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT 'Subject',
 `fs` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT 'Score',
 `time` datetime(0) NULL DEFAULT NULL COMMENT 'time',
 PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;

INSERT INTO `test_01` VALUES (1, 'X0219001', '小三', '语文', '98', '2020-08-06 15:51:21');
INSERT INTO `test_01` VALUES (2, 'X0219001', '小三', '数学', '90', '2020-07-01 15:51:25');
INSERT INTO `test_01` VALUES (3, 'x0219001', '小三', '英语', '77', '2020-06-01 15:51:28');
INSERT INTO `test_01` VALUES (4, 'X0219002', '小二', '语文', '98', '2020-08-06 15:51:21');

SELECT * FROM test_01 WHERE stu REGEXP 'X';

SELECT * FROM test_01 WHERE stu REGEXP '.9001';
SELECT * FROM test_01 WHERE stu REGEXP '.02..0';

SELECT * FROM test_01 WHERE user REGEXP '二|四';

SELECT * FROM test_01 WHERE stu REGEXP '0[23]';