多列子查询不适用于笛卡尔积答案

【问题标题】：Multiple column sub query not working with cartesian product多列子查询不适用于笛卡尔积
【发布时间】：2015-09-18 22:35:00
【问题描述】：

SELECT 
   daf.id as affiliate_id,
   daf.name as affiliate_name,
   dal.name as allocation_name,
   dal.id as allocation_id,
   dal.allocation,dal.price
FROM 
     degreeamerica.affiliates daf,degreeamerica.allocations dal
JOIN 
     (select pap.lead_price,pap.live from paul.affiliates_price pap) pafp  
ON (dal.id=pafp.allocation_id and daf.id=pafp.affiliate_id) 
ORDER BY daf.id;

未知列 pafp.allocation_id。我有这个专栏。但它不起作用。请帮忙。

【问题讨论】：

不要在from 子句中使用逗号。始终使用明确的join（即使cross join）。这将解决您的问题。
子查询中没有该列
(select pap.lead_price,pap.live,allocation_id,affiliate_id from paul.affiliates_price pap) 修复
感谢一百万 cske。

标签： mysql sql database subquery cartesian-product

【解决方案1】：

您的子查询中似乎未选择“allocation_id”列。在子查询选定列中添加此列并检查。

SELECT 
   daf.id as affiliate_id,
   daf.name as affiliate_name,
   dal.name as allocation_name,
   dal.id as allocation_id,
   dal.allocation,dal.price
FROM 
     degreeamerica.affiliates daf,degreeamerica.allocations dal
JOIN 
     (select pap.lead_price,pap.live, allocation_id from paul.affiliates_price pap) pafp  
ON (dal.id=pafp.allocation_id and daf.id=pafp.affiliate_id) 
ORDER BY daf.id;

【讨论】：