何使用最多獲得MySQL中最後一項（）

Question

我想作爲結果使用max()的最後一個項目，但我剛開始就算IM使用max()

這裏的第一個項目是在SQL代碼：

SELECT r.correct, r.items, r.percentage,MAX(r.date_taken) as date_taken, 
     u.username,u.FN, u.user_course_type, 
     IFNULL(u.user_major_type,'N/A') as user_major_type,u.level_name, 
     u.section_name 
FROM bcc_fs_exam_result r 
INNER JOIN 
(SELECT u.id_user, u.username, CONCAT(u.lastname,', ',u.firstname) as FN, 
c.user_course_type, m.user_major_type, l.level_name, s.section_name 
FROM bcc_fs_user u 
LEFT JOIN bcc_fs_user_course c on c.id_user_course = u.id_user_course 
LEFT JOIN bcc_fs_user_major m on m.id_user_major = u.id_user_major 
LEFT JOIN bcc_fs_group_level l ON l.id_level = u.id_level 
LEFT JOIN bcc_fs_group_section s ON s.id_section = u.id_section 
) u ON r.id_user = u.id_user WHERE r.id_exam = 5 GROUP BY r.id_user 

TIA

Answer 1

我從你的問題是，你想要得到「正確的」，「項」，「百分比」等。 bcc_fs_exam_result中具有最後一個或第一個日期的行的列。

如果這是正確的，那麼您可以通過首先找到每個id_user的最小或最大日期，然後將其加入考試結果表中，過濾bcc_fs_exam_result。

SELECT 
    r.correct, 
    r.items, 
    r.percentage, 
    r.date_taken, 
    u.username, 
    u.FN, 
    u.user_course_type, 
    IFNULL(u.user_major_type,'N/A') as user_major_type, 
    u.level_name, 
    u.section_name 
FROM bcc_fs_exam_result r 
INNER JOIN (

    SELECT u.id_user, 
     u.username, 
     CONCAT(u.lastname,', ',u.firstname) as FN, 
     c.user_course_type, 
     m.user_major_type, 
     l.level_name, 
     s.section_name 
    FROM bcc_fs_user u 
     LEFT JOIN bcc_fs_user_course c on c.id_user_course = u.id_user_course 
     LEFT JOIN bcc_fs_user_major m on m.id_user_major = u.id_user_major 
     LEFT JOIN bcc_fs_group_level l ON l.id_level = u.id_level 
     LEFT JOIN bcc_fs_group_section s ON s.id_section = u.id_section 

) u ON r.id_user = u.id_user 

INNER JOIN ( 
    SELECT 
     id_user, max(r.date_taken) as last_date_taken 
    FROM bcc_fs_exam_result 
    GROUP BY id_user 
) as lastdate ON lastDate.id_user = r.id_user and r.date_taken = lastdate.last_date_taken 

這可以更簡單地寫爲：

SELECT 
    r.correct, 
    r.items, 
    r.percentage, 
    r.date_taken, 
    u.username, 
    CONCAT(u.lastname,', ',u.firstname) as FN, 
    c.user_course_type, 
    IFNULL(m.user_major_type,'N/A') as user_major_type, 
    l.level_name, 
    s.section_name 
FROM bcc_fs_exam_result r 
INNER JOIN ( 
    SELECT 
     id_user, max(r.date_taken) as last_date_taken 
    FROM bcc_fs_exam_result 
    GROUP BY id_user 
) as lastdate ON lastDate.id_user = r.id_user and r.date_taken = lastdate.last_date_taken 

INNER JOIN bcc_fs_user u on r.id_user = u.id_user 
LEFT JOIN bcc_fs_user_course c on c.id_user_course = u.id_user_course 
LEFT JOIN bcc_fs_user_major m on m.id_user_major = u.id_user_major 
LEFT JOIN bcc_fs_group_level l ON l.id_level = u.id_level 
LEFT JOIN bcc_fs_group_section s ON s.id_section = u.id_section 

你認爲id_user + date_taken是bcc_fs_exam_result代理鍵，你或許應該有約束，如果在所有可能強制執行。否則，從您的樣本數據看，唯一ID列id_result的順序跟在date_taken之後，所以您可能最好使用Max(id_result)而不是Max(date_taken)。這將避免返回重複的行爲一個id_user其中兩行bcc_fs_exam_result具有相同的taken_date和`id_user。