Question

我有这些表

    Customers
    CustomerNumber    date
    001               8/1/2017
    002               8/2/2017
    003               8/3/2017

    Tags
    Index   Tag   Description 
    1       NEW    New customer
    2       OTHER  Some other tag

   Customers_Tags
   TagIndex    CustomerNumber
   1           001
   1           002
   2           002
   2           003

如何在单个查询中为所有客户提供标签1以及客户拥有的任何其他标签？因此，如果寻找标签1得到：

customer    tag    date
001         1      8/1/2017
002         1      8/2/2017
002         2      8/2/2017

Answer 1

当该客户拥有索引1的标记时，使用exists()获取所有客户和代码：

select ct.customernumber, ct.tagindex, c.date
from customers c
  inner join customers_tags ct
    on c.customernumber = ct.customernumber
where exists (
  select 1
  from customers_tags i
  where i.customernumber = ct.customernumber
    and i.tagindex = 1
  )

或使用in()：

select ct.customernumber, ct.tagindex, c.date
from customers c
  inner join customers_tags ct
    on c.customernumber = ct.customernumber
where c.customernumber in  (
  select i.customernumber
  from customers_tags i
  where i.tagindex = 1
  )

加入客户和标签表

1 个答案: