Question

我尝试从3表中查看显示DISTINCT记录的查询。但是也显示重复用户记录。

SELECT DISTINCT users.sid, users.username, users.registration_date, users.FirstName,
    users.LastName, users.phoneNumber, listings.Resume, uploaded_files.saved_file_name
FROM users JOIN listings
ON users.sid = listings.user_sid
JOIN uploaded_files
ON listings.Resume=uploaded_files.id
WHERE listings.listing_type_sid = '7' AND listings.Resume != 'NULL'

Answer 1

对表的结构做出一些大的假设。

明显的方法是加入一个获取每个用户最新上市日期的子查询，然后将其与列表相关联以获取该日期的列表字段。

SELECT users.sid, 
        users.username, 
        users.registration_date, 
        users.FirstName,
        users.LastName, 
        users.phoneNumber, 
        listings.Resume, 
        uploaded_files.saved_file_name
FROM users 
INNER JOIN
(
    SELECT user_sid, MAX(resume_date) AS latest_resume
    FROM listings
    GROUP BY user_sid
) sub0
ON users.sid = sub0.user_sid
INNER JOIN listings
ON sub0.sid = listings.user_sid
AND sub0.latest_resume = listings.resume_date
INNER JOIN uploaded_files
ON listings.Resume=uploaded_files.id
WHERE listings.listing_type_sid = '7' 
AND listings.Resume != 'NULL'

有点小提琴是使用GROUP_CONCAT获取按日期排序的所有已保存文件，然后使用SUBSTRING_INDEX获取第一个（我刚刚使用默认逗号分割文件 - 但你应该真的使用分隔的，永远不会出现在任何文件名中）

SELECT users.sid, 
        users.username, 
        users.registration_date, 
        users.FirstName,
        users.LastName, 
        users.phoneNumber, 
        listings.Resume, 
        SUBSTRING_INDEX(GROUP_CONCAT(uploaded_files.saved_file_name ORDER BY listings.resume_date DESC), ',', 1) AS saved_file_name
FROM users 
INNER JOIN listings
ON users.sid = listings.user_sid
INNER JOIN uploaded_files
ON listings.Resume=uploaded_files.id
WHERE listings.listing_type_sid = '7' 
AND listings.Resume != 'NULL'
GROUP BY users.sid, 
        users.username, 
        users.registration_date, 
        users.FirstName,
        users.LastName, 
        users.phoneNumber, 
        listings.Resume

没有在3表连接上显示DISTINCT记录

1 个答案: