sql - MySql 多次计算同一列

Question

SELECT COUNT(w.invoiceId) AS '10 Days' FROM tbl_Invoice w
WHERE w.invoiceId NOT IN(
SELECT inv.invoiceId FROM tbl_InvoiceAllocation inv)
AND w.invoiceDate < DATE_SUB(curdate(), INTERVAL 10 DAY)

它工作正常并返回日期超过 10 天前的所有发票的计数。我现在想在同一查询中返回超过 20 天和 100 天的发票计数。所以理想情况下，查询会返回如下内容:

10 Days    20 Days    100 Days

350        280        90

Answer 1

将COUNT改为SUM，将指定的WHERE子句作为CASE语句，真值为1，假值为0

有点像

SELECT  SUM( CASE WHEN w.invoiceDate < DATE_SUB(curdate(), INTERVAL 10 DAY) THEN 1 ELSE 0 END) AS '10 Days',
        SUM( CASE WHEN w.invoiceDate < DATE_SUB(curdate(), INTERVAL 20 DAY) THEN 1 ELSE 0 END) AS '20 Days'
FROM    tbl_Invoice w 
WHERE   w.invoiceId NOT IN( 
                            SELECT  inv.invoiceId 
                            FROM    tbl_InvoiceAllocation inv) 
AND     w.invoiceDate < DATE_SUB(curdate(), INTERVAL 20 DAY)