未知列问题

Question

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, pap.allocation_id,pap.affiliate_id from paul.affiliates_price pap) pafp  
ON (dal.id=pafp.allocation_id and daf.id=pafp.affiliate_id) 
ORDER BY daf.id;

问题：它在 on 子句中显示未知列 daf.id，虽然我在字段列表中有此列，请帮助！！！。

Answer 1

JOIN 链在逗号分隔表之前进行评估。一直切换到显式JOINs 就可以了。

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 
     (select pap.lead_price,pap.live, pap.allocation_id,pap.affiliate_id
      from paul.affiliates_price pap) pafp  
JOIN
     degreeamerica.affiliates daf
     ON (daf.id = pafp.affiliate_id) 
JOIN
     degreeamerica.allocations dal ON 
     ON (dal.id = pafp.allocation_id) 
ORDER BY daf.id;

Answer 2

尝试像这样编写FROM 子句：

FROM paul.affiliates_price pafp JOIN
     degreeamerica.affiliates daf
     ON daf.id = pafp.affiliate_id JOIN
     degreeamerica.allocations dal 
     ON dal.id = pafp.allocation_id 

子查询也是不必要的，它阻碍了索引的使用（在 MySQL 中）。

Answer 3

您可以将affiliates_price 表的子查询用作 FROM 和 WHERE 子句之间的表。它将以这种方式工作。

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,
    (select pap.lead_price,pap.live, pap.allocation_id,pap.affiliate_id from paul.affiliates_price pap) pafp     
WHERE
    dal.id=pafp.allocation_id and daf.id=pafp.affiliate_id
ORDER BY daf.id;