外连接内连接（编码）

鸣谢： https://blog.csdn.net/plg17/article/details/78758593

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CREATE TABLE `a_table` (
  `a_id` int(11) DEFAULT NULL,
  `a_name` varchar(10) DEFAULT NULL,
  `a_part` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8

CREATE TABLE `b_table` (
  `b_id` int(11) DEFAULT NULL,
  `b_name` varchar(10) DEFAULT NULL,
  `b_part` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8

insert into b_table value(2,"老王","秘书部");
insert into b_table value(3,"老张","设计部");
insert into b_table value(5,"老刘","人事部");
insert into b_table value(6,"老黄","生产部");

insert into a_table value(1,"老潘","总裁部");
insert into a_table value(2,"老王","秘书部");
insert into a_table value(3,"老张","设计部");
insert into a_table value(4,"老李","运营部");

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内连接：

select * from a_table a inner join b_table b on a.a_id = b.b_id;

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外连接：

左连接：
select * from a_table a left join b_table bon a.a_id = b.b_id;

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