mysql-模拟全连接处理

方案：通过union连接查询出所有需要的特殊标签，然后在通过left join与union中的结果集做多表比较。

sql 

select t.`code`,a.`count` as count_a,b.`count` as count_b from(
select `code` from tmp_a a
union
select `code`from tmp_b b) t left  join tmp_a a on t.`code`=a.`code` left join tmp_b b on t.`code`=b.`code`;

 两张表

select * from tmp_a;
select * from tmp_b;