Question

我正在尝试加入2个表，但出现错误

'非唯一表/别名：'ct'

查询是

select em.* ,ct.Cities_NAME
from Customer em,
     Cities ct inner join Cities ct on ct.Cities_ID = em.Customer_CITY 
where Customer_GROUP is NULL and Customer_ENABLED is not FALSE and Customer_TYPE != 'User'

错误在哪里，为什么？

Answer 1

从不在FROM子句中使用逗号。始终使用正确的，明确的，标准 JOIN语法：

select em.*, ct.Cities_NAME
from Customer em inner join
     Cities ct
     on ct.Cities_ID = em.Customer_CITY 
where em.Customer_GROUP is NULL and
      em.Customer_ENABLED and
      em.Customer_TYPE <> 'User';

由于某种原因，您在查询中两次列出了ct。您还应该限定查询中的所有列引用。

Answer 2

select em.* ,ct.Cities_NAME
 from Customer em , 
 Cities ct
 Where
 ct.Cities_ID = em.Customer_CITY -- it allows only matched id with city 
 and 
 Customer_GROUP is NULL  -- it accept when customer_group is null
 and 
 Customer_ENABLED not like '%FALSE%'  --it filter if customer enables is true
 and 
 Customer_TYPE not like '%User%'  -- it accepts customer type is not as user

MySQL Join-非唯一表/别名错误

2 个答案: