Question

我有一个包含交易的表格，以及一个发布最常用信用卡的声明。 AMEX，VISA ......

SELECT CARDBRAND,
   count(*) as cardused
from INFO c
left join paytb t
   on c.CONT_ID = t.CONT_ID
GROUP BY CARDBRAND
ORDER BY 2 desc;

现在我想添加一个包含商店的MERCHNAME的列，这些商店最常见于与信用卡交易中的商店：

CARDBRAND    CARDUSED        MERCHNAME
----------------------------------------
AMEX          182345         Gasstation 
VISA           70943          ....

Answer 1

SELECT CARDBRAND
  ,count(*) as cardused
  ,MERCHNAME
FROM INFO c
LEFT JOIN paytb t
    on c.CONT_ID = t.CONT_ID
GROUP BY CARDBRAND,
         MERCHNAME
ORDER BY count(*) desc;

建议：始终建议在ORDERBY子句中使用ColumnName或函数，而不是列号，以避免混淆。

Answer 2

首先，您的正确查询应为：

select c.cardbrand, count(t.cont_id) as cardused
from info c left join
     paytb t
     on c.cont_id = t.cont_id
group by c.cardbrand;

否则，对于未使用的卡品牌，您将永远不会获得“0”。

对于商家信息，您可以使用窗口功能：

select cardbrand, total_cardused, merchant
from (select c.cardbrand, t.merchant, count(t.cont_id) as cardused,
             sum(count(t.cont_id)) over (partition by c.cardbrand) as total_cardused,
             row_number() over (partition by c.cardbrand order by count(t.cont_id) desc) as seqnum
      from info c left join
           paytb t
           on c.cont_id = t.cont_id
      group by c.cardbrand, t.merchant
     ) cm
where seqnum = 1
group by c.cardbrand;

最常见的发生

2 个答案: