在组内过滤结果 sql

Question

在下面的table中，我想知道有多少顾客点了没有咖啡的午餐。结果将是 1，销售 ID 300，因为订购了两份午餐，但只订购了一份咖啡。

距离上次使用已经8年了SQL！我怎么说“按销售 ID 对记录进行分组，对于每个组，删除没有午餐或 COUNT(coffee) < COUNT(lunch) 的组”？

SALE ID	Product
100	coffee
100	lunch
200	coffee
300	lunch
300	lunch
300	coffee

Answer 1

这是一种方法：

select count(*) from (
   select saleID 
   from tablename
   group by saleID
   having sum(case when product ='coffee' then 1 else 0 end) = 0 
   and sum(case when product ='lunch' then 1 else 0 end) = 1
) t

Answer 2

您可以使用聚合和 HAVING 子句中的条件来完成。

这个查询：

SELECT sale_id
FROM tablename
GROUP BY sale_id
HAVING SUM(product = 'lunch') > SUM(product = 'coffee');

returns 所有你想要的 sale_id。

这个查询：

SELECT DISTINCT COUNT(*) OVER () counter
FROM tablename
GROUP BY sale_id
HAVING SUM(product = 'lunch') > SUM(product = 'coffee');

returns 您想要的 sale_id 个数。

参见demo。

Answer 3

select count(*) from (
  --in this subquery calculate counts and ignore items that haven't any lunch
   select 
    saleID, sum(case when product ='coffee' then 1 else 0 end) as coffee,
    sum(case when product ='lunch' then 1 else 0 end)  lunch
   from tablename
   group by saleID
   having sum(case when product ='lunch' then 1 else 0 end) >= 1  --Here we are ignoring all items haven't any lunch
) t
where lunch > coffee -- we check second condition be ok

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