最常見的發生

Question

我有一個表中有交易和發表最常用的信用卡的聲明。 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; 

現在我想用的店鋪MERCHNAME是最經常在一個事務中找到具有的信用卡添加一列：

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; 

建議：總是建議在ORDERBY子句中使用ColumnName或函數，而不是列號，以避免混淆。

Answer 2

首先，你正確的查詢應該是：

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; 

否則，你將永遠不會得到「0」爲未使用的支付卡品牌。

對於商戶信息，您可以使用窗口函數：

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;