如何優化此sql查詢？

Question

這裏有4個表....

1. tbl_std_working_hour
2. tbl_attendance
3. tbl_holiday
4. tbl_leave

我想找出這個查詢員工缺勤報告... 。但是，當我爲許多員工應用此功能時，需要時間......有什麼方法可以簡化此查詢？

SELECT date 
FROM tbl_std_working_hour 
WHERE date NOT IN (SELECT date FROM tbl_attendance WHERE emp_id = '$emp_id') 
AND date NOT IN (SELECT date FROM tbl_holiday) 
AND date NOT IN (SELECT date FROM tbl_leave WHERE emp_id = '$emp_id') 
AND total_hour <> '00:00:00' 
AND date >= '$start' 
AND date <= '$end' 
AND emp_id = '$emp_id' 

Answer 1

首先，我的rewrite使用NOT EXISTS：

SELECT wh.date 
FROM tbl_std_working_hour wh 
WHERE NOT EXISTS (SELECT 1 
        FROM tbl_attendance a 
        WHERE a.date = wh.date AND a.emp_id = wh.emp_id 
       ) AND 
     NOT EXISTS (SELECT 1 
        FROM tbl_holiday h 
        WHERE h.date = wh.date 
       ) AND 
     NOT EXISTS (SELECT 1 
        FROM tbl_leave l 
        WHERE l.emp_id = wh.emp_id and l.date = wh.date 
       ) 
WHERE wh.total_hour <> '00:00:00' AND 
     wh.date >= '$start' AND 
     wh.date <= '$end' AND 
     wh.emp_id = '$emp_id'; 

然後添加以下的複合（多列）的索引：

• tbl_std_working_hour(emp_id, date, total_hour)
• tbl_attendance(emp_id, date)
• tbl_holiday(date)（可能已經如果存在是date主鍵或唯一）
• tbl_leave(emp_id)（可能已經存在，如果emp_id是主鍵或唯一）

注意，我改變了查詢，以便參考emp_id外部查詢。這使得更容易更改emp_id。另外，您的查詢應該使用WHERE子句中的值的參數。

Answer 2

這也是一種更好的方式，可以更好地利用工作UNION ALL

SELECT date 
FROM tbl_std_working_hour AS tswh 
WHERE NOT EXISTS(
    SELECT date FROM tbl_attendance ta WHERE ta.date = tswh.date AND ta.emp_id = tswh.emp_id 
    UNION ALL 
    SELECT date FROM tbl_holiday th WHERE th.date = tswh.date 
    UNION ALL 
    SELECT date FROM tbl_leave tl WHERE tl.date = tswh.date AND tl.emp_id = tswh.emp_id) 
AND total_hour <> '00:00:00' 
AND date >= '$start' 
AND date <= '$end' 
AND emp_id = '$emp_id'