SQL使用相同的字段两次以不同的标准

Question

我有一个头计数（voucher_credits.voucher_id），我已经使用WHERE语句将其添加到我的报告中，但我想再次添加它作为另一列使用不同的标准，我该怎么做？

SELECT vouchers.code, vouchers.credit, count(voucher_credits.voucher_id) as Activated 
FROM vouchers, voucher_credits, users 
WHERE vouchers.id = voucher_credits.voucher_id 
    AND voucher_credits.remaining_credit = 0 
    AND users.id = voucher_credits.user_id AND users.state = 'active' 
    AND vouchers.is_customer_service = FALSE 
GROUP by vouchers.code, vouchers.credit 
ORDER by count(voucher_credits.voucher_id) DESC 
LIMIT 100 

第二列是users.state = '取消'，不.remaining_credit = 0

Answer 1

尝试UNION ALL：

SELECT vouchers.code, vouchers.credit, count(voucher_credits.voucher_id) as Activated 
FROM vouchers, voucher_credits, users 
WHERE vouchers.id = voucher_credits.voucher_id 
    AND voucher_credits.remaining_credit = 0 
    AND users.id = voucher_credits.user_id AND users.state = 'active' 
    AND vouchers.is_customer_service = FALSE 
GROUP by vouchers.code, vouchers.credit 
ORDER by count(voucher_credits.voucher_id) DESC 
UNION ALL 
SELECT vouchers.code, vouchers.credit, count(voucher_credits.voucher_id) as Activated 
FROM vouchers, voucher_credits, users 
WHERE vouchers.id = voucher_credits.voucher_id 
    AND users.state = 'cancelled' 
    AND users.id = voucher_credits.user_id AND users.state = 'active' 
    AND vouchers.is_customer_service = FALSE 
GROUP by vouchers.code, vouchers.credit 
ORDER by count(voucher_credits.voucher_id) DESC 

Answer 2

如果所有的数据都来自同一行，你可以使用“条件和”计数，这基本上是基于表达式添加0或1的位置：

SELECT ..., 
    SUM(CASE WHEN voucher_credits.remaining_credit = 0 AND users.state = 'active' 
     THEN 1 ELSE 0 END) Activated, 
    SUM(CASE WHEN users.state = 'cancelled' THEN 1 ELSE 0 END) CanceledUser, 
FROM ... 
... 

使用您的查询，这将是：

SELECT vouchers.code, vouchers.credit, 
    SUM(CASE WHEN voucher_credits.remaining_credit = 0 AND users.state = 'active' 
     THEN 1 ELSE 0 END) Activated, 
    SUM(CASE WHEN users.state = 'cancelled' THEN 1 ELSE 0 END) CanceledUser, 
FROM vouchers 
INNER JOIN voucher_credits ON vouchers.id = voucher_credits.voucher_id 
INNER JOIN users ON users.id = voucher_credits.user_id 
WHERE vouchers.is_customer_service = FALSE 
GROUP by vouchers.code, vouchers.credit 
ORDER by Activated DESC 
LIMIT 100 

Answer 3

您可以加入表格两次。如果您从2个子查询中获得不同的记录，我使用了FULL OUTER JOIN。随意更改联接类型。

select t1.code, t1.credit, t1.Activated, t2.code, t2.credit, t2.Cancelled 
from 
(SELECT vouchers.code, vouchers.credit, count(voucher_credits.voucher_id) as Activated 
FROM vouchers, voucher_credits, users 
WHERE vouchers.id = voucher_credits.voucher_id 
    AND voucher_credits.remaining_credit = 0 
    AND users.id = voucher_credits.user_id AND users.state = 'active' 
    AND vouchers.is_customer_service = FALSE 
GROUP by vouchers.code, vouchers.credit) t1 
FULL OUTER JOIN 
(SELECT vouchers.code, vouchers.credit, count(voucher_credits.voucher_id) as Cancelled 
FROM vouchers, voucher_credits, users 
WHERE vouchers.id = voucher_credits.voucher_id 
    AND users.state = 'cancelled' 
    AND users.id = voucher_credits.user_id AND users.state = 'active' 
    AND vouchers.is_customer_service = FALSE 
GROUP by vouchers.code, vouchers.credit) t2 
ON t1.code = t2.code and t1.credit = t2.credit