--- ==================== 先把数据导入数据库
CREATE TABLE `test_join_where_a` (
`aid` int(0) NOT NULL,
`aname` varchar(255) ,
`atimedate` datetime(0) ,
`ascore` varchar(255)
);
INSERT INTO `test_join_where_a`(`aid`, `aname`, `atimedate`, `ascore`) VALUES (1, '张三', '2023-05-03 01:13:30', '80');
INSERT INTO `test_join_where_a`(`aid`, `aname`, `atimedate`, `ascore`) VALUES (2, '李四', '2023-06-22 01:15:09', '85');
INSERT INTO `test_join_where_a`(`aid`, `aname`, `atimedate`, `ascore`) VALUES (3, '王五', '2023-04-27 01:15:28', '78');
INSERT INTO `test_join_where_a`(`aid`, `aname`, `atimedate`, `ascore`) VALUES (4, '赵六', '2023-01-26 01:15:52', '68');
CREATE TABLE `test_join_where_b` (
`bid` int(0) NOT NULL,
`bname` varchar(255) ,
`btimedate` datetime(0) ,
`bscore` varchar(255)
);
INSERT INTO `test_join_where_b`(`bid`, `bname`, `btimedate`, `bscore`) VALUES (1, '张三', '2023-05-03 01:13:30', '80');
INSERT INTO `test_join_where_b`(`bid`, `bname`, `btimedate`, `bscore`) VALUES (2, '李四', '2023-06-22 01:15:09', '85');
INSERT INTO `test_join_where_b`(`bid`, `bname`, `btimedate`, `bscore`) VALUES (3, '王五1', '2023-04-27 01:15:28', '78');
INSERT INTO `test_join_where_b`(`bid`, `bname`, `btimedate`, `bscore`) VALUES (4, '赵六', '2023-01-26 01:15:52', '68');
-- =================================
结论是：on 后面的and ，left join 与 right join 都是有效的。当把and换成where 后，left join 与 right join 功能失效了，这是sql 的执行的顺序造成的。
2、sql的执行顺序
2.1、SQL的执行顺序_sql执行顺序优先级_洛禾符的博客-CSDN博客SQL的执行顺序_sql执行顺序优先级https://blog.csdn.net/luohefu1/article/details/122534905
