inner join & outer join 专题

1. inner join：

在店铺表中找到含商品表中所有商品的店铺：

select shopfrom items,shopitemswhere items.item = shopitems.itemgroup by shophaving count(*) = (select count(*) from items)

---针对集合设定条件：inner join 过滤出品类相同的记录；having 条件为聚合后两表品类数一致。

2. outer join：

在店铺表中找到仅含商品表中所有商品的店铺：

select shopfrom shopitems left join itemson shopitems.item = items.itemgroup by shophaving count(items.item) = (select count(*) from items)

---对 left join 匹配到的右列品类计数，条件为与商品表品类数一致。 

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