MySQL WHERE子查询与比较运算符

我试图从订单表中检索客户和发票ID列表，其中客户只有一个订单。下面的SQL返回零记录，应该有几十个。如果我用一个有效的userid替换它，子查询似乎可以正常工作。我必须做一些非常错误的事情，有什么帮助吗？MySQL WHERE子查询与比较运算符

SELECT tblclients.id AS clientid, tblinvoices.id AS invoiceid 
      FROM tblorders 
      join tblinvoices ON tblorders.invoiceid = tblinvoices.id 
      join tblclients ON tblorders.userid = tblclients.id 
      WHERE (SELECT COUNT(*) FROM tblorders WHERE userid = tblorders.userid) = 1;

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2012-08-03 Michelle

什么是你想实现这一点：'WHERE（SELECT COUNT（*）FROM tblorders其中userid = tblorders.userid）= 1' – mlishn 2012-08-03 16:24:53

其中与相关的订单数量客户端是一个。 – Michelle 2012-08-04 09:15:38

是否会导致“1 = 1”或“0 = 1”或其他组合？ – mlishn 2012-08-05 01:41:14

我想你有一个别名的问题。尝试添加T1别名：

SELECT tblclients.id AS clientid, tblinvoices.id AS invoiceid 
      FROM tblorders T1 
      join tblinvoices ON T1.invoiceid = tblinvoices.id 
      join tblclients ON T1.userid = tblclients.id 
      WHERE (SELECT COUNT(*) FROM tblorders WHERE userid = T1.userid) = 1;

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2012-08-03 16:24:51

MySQL WHERE子查询与比较运算符

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