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我试图在没有运气的情况下实现 MySQL 的 FULL JOIN 版本。我的结果需要包括来自“用户”的所有行，无论用户在其他表中是否有匹配的行。现在我的结果并不全是由于 LEFT JOIN 的性质，但是当我 UNION ALL、LEFT 和 RIGHT 时，我的结果会进一步缩小。

SELECT 
    users.*, profile_status.*, photos.*, general.*, experience.*, occupation.*, 
    flagged.*, last_update.*, job_search.*, users.user_id AS userID, 
    user_profile_status.user_id AS profileID
FROM users
    JOIN profile_status ON users.user_id = profile_status.user_id
    LEFT JOIN photos ON users.user_id = photos.user_id AND photos.selected = 1
    LEFT JOIN general ON users.user_id = general.user_id
    LEFT JOIN occupation ON users.user_id = occupation.user_id
    LEFT JOIN experience ON users.user_id = experience.user_id
    LEFT JOIN flagged ON users.user_id = flagged.user_id
    LEFT JOIN job_search ON users.user_id = job_search.user_id
    LEFT JOIN last_update ON users.user_id = last_update.user_id
WHERE 
    users.approved = 1 AND users.admin_level = 0
ORDER BY last_update.last_update DESC

我对 UNION 的尝试

SELECT 
    users.*, profile_status.*, photos.*, general.*, experience.*, occupation.*, 
    flagged.*, last_update.*, job_search.*, users.user_id AS userID, 
    user_profile_status.user_id AS profileID
FROM users
    JOIN profile_status ON users.user_id = profile_status.user_id
    LEFT JOIN photos ON users.user_id = photos.user_id AND photos.selected = 1
    LEFT JOIN general ON users.user_id = general.user_id
    LEFT JOIN occupation ON users.user_id = occupation.user_id
    LEFT JOIN experience ON users.user_id = experience.user_id
    LEFT JOIN flagged ON users.user_id = flagged.user_id
    LEFT JOIN job_search ON users.user_id = job_search.user_id
    LEFT JOIN last_update ON users.user_id = last_update.user_id
UNION ALL
    SELECT 
    users.*, profile_status.*, photos.*, general.*, experience.*, occupation.*, 
    flagged.*, last_update.*, job_search.*, users.user_id AS userID, 
    user_profile_status.user_id AS profileID
FROM users
    JOIN profile_status ON users.user_id = profile_status.user_id
    RIGHT JOIN photos ON users.user_id = photos.user_id AND photos.selected = 1
    RIGHT JOIN general ON users.user_id = general.user_id
    RIGHT JOIN occupation ON users.user_id = occupation.user_id
    RIGHT JOIN experience ON users.user_id = experience.user_id
    RIGHT JOIN flagged ON users.user_id = flagged.user_id
    RIGHT JOIN job_search ON users.user_id = job_search.user_id
    RIGHT JOIN last_update ON users.user_id = last_update.user_id
WHERE 
    users.approved = 1 AND users.admin_level = 0
ORDER BY last_update.last_update DESC

表结构：

Table users
user_id  first_name   last_name   admin_level   user_approved  
1        tommy        jones       0             1      
2        johnny       rocket      0             1      
3        sally        hotpants    0             1  

Table profile_status
user_id  photo_uploaded   
1        1
2        1
3        1

Table photos
photo_id  user_id  filename      selected
1         1        photo_1.jpg   1
2         2        photo_2.jpg   0
3         2        photo_2.jpg   1
4         3        photo_3.jpg   1

Table general
user_id  city        state      zip     neighborhood
1        baltimore   maryland   00125   hamsterdam
2        lakeland    maine      11542   treemont
2        tipper      vermont    08483   NULL

Table experience
user_id  waldorf  kumon  homeschooling 
1        0       1       0
2        0       0       1

Table occupation
user_id  occupation 
1        teacher  
2        student    
3        student 

Table job_search
search_id  user_id  job
1          1        art teacher  
2          2        designer 

Table flagged
user_id  flagged 
1        1  
2        0    

Table last_update
update_id  user_id  last_update           photo_update
1          1        0000-00-00 00:00:00   0000-00-00 00:00:00
2          2        0000-00-00 00:00:00   0000-00-00 00:00:00
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