警告：子查詢返回超過 1 行

Question

當我運行此查詢時

SELECT a.sname,a.date,a.Roll_Number,b.branch,
                            COUNT(DISTINCT a.date) AS totaldays,

                            (SELECT COUNT(a.attendance_status)
                            FROM attendance as a , branch as b  
                            WHERE a.attendance_status='Present' and b.id='".$_GET['id']."' and  a.branch=b.branch  GROUP BY a.sid )
                             as present_days
                             FROM attendance as a , branch as b  
                             WHERE b.id='".$_GET['id']."'
                            and  a.branch=b.branch
                            GROUP BY a.sname ";

它顯示了這個錯誤

警告：mysqli::query()：(21000/1242)：子查詢返回超過 1 行

幫我更正這個查詢。 先感謝您

Answer 1

查看您的查詢似乎您不需要present_days的子查詢，並且避免使用此子查詢，您應該避免錯誤..

SELECT a.sname
  ,a.date,a.Roll_Number
  ,b.branch,
  COUNT(DISTINCT a.date) AS totaldays,
  COUNT(a.attendance_status) as present_days
  FROM attendance as a 
  INNER JOIN branch as b   ON a.attendance_status='Present' 
      and b.id='".$_GET['id']."' 
          and  a.branch=b.branch  
  GROUP BY a.sid 

無論如何，你會面臨 sqlinjection 的風險.. 你不應該在 sql 中使用 php var，而是使用准備好的語句和綁定參數 ..