SQL：添加一列，分爲類別

Question

我有具有transaction_id作爲主鍵的表，並且還包含customer_id這是一個外鍵。

現在有一列type它有兩個值：'Card'和'cash'。

現在的一些客戶已經用於支付這兩種方法。我想添加一個新欄目並將客戶分類爲「Only card」，「Only cash」和「Both」。

Transaction id  Customer id Type 
1     100   Card 
2     101   Cash 
3     102   Card 
4     103   Cash 
5     101   Card 

所以在這個表我想要一個新列「支付類型」進行分類客戶101既是因爲他已經使用這兩種支付方式。

Answer 1

而不是增加一列的表格，如果你想要做的是分析的付款方式，然後做這樣的事情可能會更好：

SELECT DISTINCT Table1.[Customer ID], T1.* 
FROM Table1 
CROSS APPLY (SELECT SUM(CASE WHEN [Type] = 'Cash' THEN 1 ELSE 0 END) AS Cash, 
      SUM(CASE WHEN [Type] = 'Card' THEN 1 ELSE 0 END) AS Card 
      FROM Table1 T WHERE T.[Customer ID] = Table1.[Customer ID]) T1 

爲您提供了這樣的結果：

CUSTOMER ID CASH CARD 
100   0  1 
101   1  1 
102   0  1 
103   1  0 

Answer 2

您可以使用窗口函數：

select t.*, 
     (case when min(type) over (partition by customerid) = max(type) over (partition by customerid) 
      then 'Only ' + min(type) over (partition by customerid) 
      else 'both' 
     end) 
from transactions t; 

Answer 3

你可以做的更好，並刪除了一下redondancy（僅值現金和卡將只在表中重複，在這種情況下，我們更喜歡重複的ID ）。所以，你可以創建例如payement_methods表格中，將有2列例如id和method，你將與你剛纔提到的三個選項填充它（只收現金，卡而已，兩者都有），你必須在你的transaction table一個例如列payment_method_id（而不是您使用的類型列）。

例如

|id  | method  | 
|1  | Cash only | 
|2  | Card Only | 
|3  | Both   | 

事務表

|id  | other columns ...|payement method | 
|1  | other columns ...|1    | 
|2  | other columns ...|3    | 
//... 

對不起我的英語，好運氣。

Answer 4

Create table tran1(Transactionid int , Customerid int , Type varchar(100)) 

insert into tran1(Transactionid , Customerid , Type) values 
(1   ,   100 ,  'Card '), 
(2   ,   101 ,  'Cash'), 
(3   ,   102 ,  'Card '), 
(4   ,   103 ,  'Cash '), 
(5   ,   101 ,  'Card ') 

alter table tran1 add NewType varchar(100) 



Update tran1 set NewType ='Only card' where Customerid IN (
select d.custid from (
select Customerid as custid,SUM(case when [Type]='Card' then 1 else 0 end) card 
,SUM(case when [Type]='Cash' then 1 else 0 end) cash 
from tran1 
group by Customerid)d 
where d.card=1 
) 


Update tran1 set NewType ='Only Cash' where Customerid IN (
select d.custid from (
select Customerid as custid,SUM(case when [Type]='Card' then 1 else 0 end) card 
,SUM(case when [Type]='Cash' then 1 else 0 end) cash 
from tran1 
group by Customerid)d 
where d.cash=1 
) 

Update tran1 set NewType ='Both' where Customerid IN (
select d.custid from (
select Customerid as custid,SUM(case when [Type]='Card' then 1 else 0 end) card 
,SUM(case when [Type]='Cash' then 1 else 0 end) cash 
from tran1 
group by Customerid)d 
where d.card=1 and cash=1 
)