为什么这会让外部联接查询拒绝在phpMyAdmin中完成？

Question

编辑：所以查询确实有效，但在我的localhost机器上运行需要一分钟。 不可否认，我的本地主机上的表格相当大（每个大约8000行），但在生产中，每个表格的行数可能超过25,000行。 有没有办法优化这个，所以它不需要那么长时间？ 如其中一条评论所示，两个表都已编入索引。

我有两个表，jos_eimcart_customers_addresses和jos_eimcart_customers。 我想从customers表中提取所有记录，并在地址表中包含可用的地址信息。 我有我认为是一个相当普通的左外连接查询，但它在phpMyAdmin中保持超时，即使它没有那么多应该找到的结果。 任何人都可以指出我做错了什么吗？ 我没有收到mySQL错误。

select 
    c.firstname,
    c.lastname,
    c.email as customer_email, 
    a.email as address_email,
    c.phone as customer_phone,
    a.phone as address_phone,
    a.company,
    a.address1,
    a.address2,
    a.city,
    a.state,a.zip, 
    c.last_signin
from jos_eimcart_customers c
    left outer join  jos_eimcart_customers_addresses a  
    on c.id = a.customer_id  
order by c.last_signin desc

Answer 1

你需要一个group by子句：

SELECT 
  c.firstname, 
  c.lastname, 
  c.email AS customer_email, 
  a.email AS address_email, 
  c.phone AS customer_phone, 
  a.phone AS address_phone, 
  a.company, 
  a.address1, 
  a.address2, 
  a.city, 
  a.state, 
  a.zip, 
  c.last_signin 
FROM jos_eimcart_customers c 
LEFT OUTER JOIN jos_eimcart_customers_addresses a ON c.id = a.customer_id 
GROUP BY 
  c.firstname, 
  c.lastname, 
  c.email AS customer_email, 
  a.email AS address_email, 
  c.phone AS customer_phone, 
  a.phone AS address_phone, 
  a.company, 
  a.address1, 
  a.address2, 
  a.city, 
  a.state, 
  a.zip, 
  c.last_signin 
ORDER BY c.last_signin DESC

Answer 2

您的查询没有任何问题（假设计数与您说的一样）。 你的服务器还有其他东西在进行。

它有机会等待锁吗？