MySQL WHERE子查詢與比較運算符

我試圖從訂單表中檢索客戶和發票ID列表，其中客戶只有一個訂單。下面的SQL返回零記錄，應該有幾十個。如果我用一個有效的userid替換它，子查詢似乎可以正常工作。我必須做一些非常錯誤的事情，有什麼幫助嗎？MySQL WHERE子查詢與比較運算符

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

什麼是你想實現這一點：'WHERE（SELECT COUNT（*）FROM tblorders其中userid = tblorders.userid）= 1' – mlishn 2012-08-03 16:24:53

其中與相關的訂單數量客戶端是一個。 – Michelle 2012-08-04 09:15:38

是否會導致「1 = 1」或「0 = 1」或其他組合？ – mlishn 2012-08-05 01:41:14

我想你有一個別名的問題。嘗試添加T1別名：

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;

來源

2012-08-03 16:24:51

MySQL WHERE子查詢與比較運算符

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