MySQL 联合查询 union

-- 合并多个查询结果集并过滤掉重复的数据
union
-- 直接合并多个查询结果集
union all

CREATE TABLE `user` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '用户id',
`name` varchar(60) DEFAULT NULL COMMENT '昵称',
`gender` tinyint(1) DEFAULT NULL COMMENT '性别 0 女 1 男 2 未知',
PRIMARY KEY (`id`)
) ENGINE=InnoDB COMMENT='用户表';
INSERT INTO `user` (`id`, `name`, `gender`) VALUES (1, '李易峰', 1);
INSERT INTO `user` (`id`, `name`, `gender`) VALUES (2, '王冰冰', 0);
INSERT INTO `user` (`id`, `name`, `gender`) VALUES (3, '谷爱凌', 0);
INSERT INTO `user` (`id`, `name`, `gender`) VALUES (4, '王心凌', 0);
INSERT INTO `user` (`id`, `name`, `gender`) VALUES (5, '薛之谦', 1);
CREATE TABLE `article` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT COMMENT '主键',
`user_id` int(11) DEFAULT NULL COMMENT '用户id',
`title` varchar(255) DEFAULT NULL COMMENT '文章标题',
`clicks` int(11) DEFAULT NULL COMMENT '点击量',
PRIMARY KEY (`id`)
) ENGINE=InnoDB COMMENT='文章表';
INSERT INTO `article` (`id`, `user_id`, `title`, `clicks`) VALUES (1, 5, '你还想要我怎样', 120);
INSERT INTO `article` (`id`, `user_id`, `title`, `clicks`) VALUES (2, 1, '古剑奇谭', 80);
INSERT INTO `article` (`id`, `user_id`, `title`, `clicks`) VALUES (3, 4, '爱你', 200);

-- 查询所有女生用户
select id,name,gender from user where gender = 0;
-- 查询发布的文章点击量超过 100 的用户
select u.id,u.name,u.gender from article a
inner join user u
on a.user_id = u.id
where a.clicks > 100;

select id,name,gender from user where gender = 0
union all
select u.id,u.name,u.gender from article a
inner join user u
on a.user_id = u.id
where a.clicks > 100;