如何在 JOIN MySQL 中进行 GROUP BY 和 COUNT(*)

Posted 2023-02-16

【中文标题】如何在 JOIN MySQL 中进行 GROUP BY 和 COUNT(*)

【英文标题】：How to do GROUP BY and COUNT(*) in JOIN MySQL

【发布时间】：2021-03-25 11:58:08

【问题描述】：

我有名为 company、product、purchase_order、skid、process_record 的表，我想要 mysql 查询结果如下。

我试过了

SELECT s.id as skidId, s.skidBarcode, po.poNumber, s.companyId, c.companyName, p.productId , p.productName, totalProcessed 
FROM skid s 
INNER JOIN company c ON s.companyId = c.id 
INNER JOIN purchase_order po on s.purchaseOrderId = po.id 
INNER JOIN product prdct on p.productId = prdct.id 
LEFT JOIN (SELECT skidID, productId , COUNT(*) as processedQuantity FROM process_record GROUP BY productId ) p ON p.skidID= s.id 
WHERE s.status = 'closed' ORDER By s.companyId,s.id

但是，此查询结果在某些行上将处理的数量计数为 NULL 和随机错误计数。

如何获得所需的 MySQL 查询输出，如屏幕截图所示？

【问题讨论】：

见meta.***.com/questions/333952/…

【参考方案1】：

我添加了GROUP BY skidID, productId 而不是GROUP BY productId，它解决了这个问题。

 SELECT s.id as skidId, s.skidBarcode, po.poNumber, s.companyId, c.companyName, p.productId , p.productName, totalProcessed 
    FROM skid s 
LEFT JOIN (SELECT skidID, productId , COUNT(*) as processedQuantity FROM process_record GROUP BY skidID, productId ) p ON p.skidID= s.id 
    INNER JOIN company c ON s.companyId = c.id 
    INNER JOIN purchase_order po on s.purchaseOrderId = po.id 
    INNER JOIN product prdct on p.productId = prdct.id 
    
    WHERE s.status = 'closed' ORDER By s.companyId,s.id

【讨论】：

选择 s.id 作为skidId，s.barCode，po.orderNumber，s.skidContent，s.companyId，s.close_status，c.companyName，IFNULL(p.productId,0) 作为productId， IFNULL(p.processedQuantity,0) as processesQuantity FROM skid s LEFT JOIN (SELECT skidID, productId, COUNT(*) as processesQuantity FROM process_record GROUP BY skidID, productId ) p ON p.skidID= s.id INNER JOIN company c ON s .companyId = c.id INNER JOIN purchase_order po on s.purchaseOrderId = po.id WHERE s.close_status != 'ClosedAndInvoiced' ORDER By s.companyId,s.id