MySQL中多个left join on关联条件的顺序说明

SELECT
	* 
FROM
	( SELECT report_date reportDate FROM tb_more_left_join mlj GROUP BY mlj.report_date ) mix
	LEFT JOIN (
SELECT
	mlj.report_date maxReportDate,
	GROUP_CONCAT( mlj.user_name ) maxUserNames,
	a.maxScore 
FROM
	tb_more_left_join mlj
	LEFT JOIN ( SELECT report_date, MAX( chinese_score ) maxScore FROM tb_more_left_join mlj GROUP BY mlj.report_date ORDER BY NULL ) a ON mlj.report_date = a.report_date 
WHERE
	mlj.chinese_score = a.maxScore 
GROUP BY
	mlj.report_date 
	) mx ON mix.reportDate = mx.maxReportDate
	LEFT JOIN (
SELECT
	mlj.report_date minReportDate,
	GROUP_CONCAT( mlj.user_name ) minUserNames,
	a.minScore 
FROM
	tb_more_left_join mlj
	LEFT JOIN ( SELECT report_date, MIN( math_score ) minScore FROM tb_more_left_join mlj GROUP BY mlj.report_date ORDER BY NULL ) a ON mlj.report_date = a.report_date 
WHERE
	mlj.math_score = a.minScore 
GROUP BY
	mlj.report_date 
	) mn ON mix.reportDate = mn.minReportDate

CREATE TABLE `tb_more_left_join`  (
  `id` int(11) NOT NULL,
  `report_date` date NULL DEFAULT NULL,
  `user_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `math_score` int(255) NULL DEFAULT NULL,
  `chinese_score` int(255) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `tb_more_left_join` VALUES (1, '2019-12-01', '盲僧', 70, NULL);
INSERT INTO `tb_more_left_join` VALUES (2, '2019-12-01', '薇恩', 100, NULL);
INSERT INTO `tb_more_left_join` VALUES (3, '2019-12-02', '赵信', 30, 60);
INSERT INTO `tb_more_left_join` VALUES (4, '2019-12-02', '琴女', NULL, 100);
INSERT INTO `tb_more_left_join` VALUES (5, '2019-12-03', '蛮王', 50, 100);
INSERT INTO `tb_more_left_join` VALUES (6, '2019-12-03', '艾希', 100, 100);
INSERT INTO `tb_more_left_join` VALUES (7, '2019-12-03', '亚索', 60, 90);

SELECT * 
FROM userinfo AS u ,jobinfo AS j 
WHERE u.userProfession=j.professionRequire
AND j.professionRequire='程序员'

SELECT * 
FROM userinfo AS u 
LEFT JOIN   
jobinfo AS j 
ON u.userProfession=j.professionRequire
AND j.professionRequire='程序员'

SELECT * 
FROM userinfo AS u 
LEFT JOIN   
(SELECT *  FROM jobinfo  WHERE jobinfo.professionRequire='程序员') AS j 
ON 
u.userProfession=j.professionRequire

SELECT * 
FROM userinfo AS u 
LEFT JOIN   jobinfo AS j 
ON u.userProfession=j.professionRequire
WHERE j.professionRequire='程序员'