UPDATE t_user ?
SET signed_time = create_time?

UPDATE t_user u1, t_user u2?
SET u1.signed_time = u2.create_time, ?
? ? u2.create_time = u1.signed_time ?

-- 同一個表
UPDATE table_a SET A=(SELECT B FROM (SELECT * FROM table_a) b WHERE b.id = table_a.id)
-- 兩個(一樣的)表
UPDATE table_a SET A = (SELECT B FROM table_b WHERE table_b.id= table_a.id)
-- 例子
-- UPDATE FY_MEDICINE_DIRECTION SET MEDICINE_NAME=(SELECT COMMON_NAME FROM (SELECT * FROM FY_MEDICINE_DIRECTION) b WHERE b.id = FY_MEDICINE_DIRECTION.id) WHERE  SOURCES='參考《國家醫(yī)保藥品手冊》（2017版）' AND MED_ISTATUS=1
-- UPDATE message  SET image=(SELECT istatus FROM (SELECT * FROM message) b WHERE b.id = message.id)

CREATE TABLE `test`  (
  `id` int(10) UNSIGNED NOT NULL AUTO_INCREMENT,
  `value` varchar(100) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 8 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of test
-- ----------------------------
INSERT INTO `test` VALUES (1, 'a');
INSERT INTO `test` VALUES (2, 'b');
INSERT INTO `test` VALUES (3, 'c');
INSERT INTO `test` VALUES (4, 'd');
INSERT INTO `test` VALUES (5, 'e');

UPDATE test SET value = id;
-- 若有其他條件往后面添加就行 update table set field1 = field2 where ...

update A inner join(select id,name from B) c on A.id = c.id set A.name = c.name;