MySql 怎么实现级联查询

首先能实现目的的语法是这么写：

select id,name,a_rankfrom table_a,(select a_id,count(*) as a_rankfrom table_bgroup by a_id)where table_a.id = table_b.a_idorder by a_rank

联合查询分为左联、内联、右联，

左联：select a.xxx,b.ccc from tableA a left join tableB b on a.id=b.id

内联：select a.xxx,b.ccc from tableA a inner join tableB b on a.id=b.id

右联：select a.xxx,b.ccc from tableA a right join tableB b on a.id=b.id

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