如何讓現在和缺勤的學生都學習一年

Question

我需要得到總數。 一年的出席人數和缺席人數：這是我的查詢：

SELECT if( status = 'P',count(level_id), 0) AS present, 
       if(status='A',count(student_id), 0) AS Absent 
        FROM attendance WHERE level_id = 'L1' AND date LIKE '2016%'

但這將返回總數。 的學生出席或缺席的部分。

Answer 1

問題是您誤解了COUNT(...)在查詢中的作用。 如果您真的想根據缺席或在場進行計數，則可以在內部有條件的情況下使用SUM(...) 。

SELECT
    SUM(if(status = 'P', 1, 0)) AS Present
    SUM(if(status = 'A', 1, 0)) AS Absent
FROM
    attendance
WHERE
    level_id = 'L1' AND date LIKE '2016%'

Answer 2

如果需要計算元素，則返回1：

 SELECT SUM(if( status = 'P',1, 0)) AS present, SUM(if(status='A',1, 0)) AS Absent
 FROM attendance WHERE level_id = 'L1' AND date LIKE '2016%'

Answer 3

嘗試使用group by子句，例如：

SELECT 
 status, 
 count(student_id) as attendance 
FROM attendance 
WHERE level_id = 'L1' 
  AND date LIKE '2016%' 
GROUP BY status;

它將為您提供表中每種狀態的計數

Answer 4

這將起作用：

SELECT DISTINCT(student_name), SUM(status = 'P') AS present, SUM(status='A') AS Absent FROM attendance GROUP BY student_name where date LIKE '2016%'