mysql UNION重复项

Question

我正在使用此mysql查询并对其进行排序，我已添加bool列is_main（是否来自主表）。结果是工作，但我得到重复，因为is_main列..有没有解决这个问题？ 查询：

SELECT 
    b.dateTime, 
    a.id, 
    a.jobName, 
    a.is_main 
FROM job_data a, data b 
WHERE a.userEmail = b.userEmail AND a.userEmail = :email 
UNION 
SELECT 
    b.dateTime, 
    b.id, 
    b.jobName, 
    b.is_main 
FROM job_data a, data b 
WHERE a.userEmail = b.userEmail AND a.userEmail = :email 

ORDER BY is_main DESC 

的job_data表：

id | dateTime | jobName | is_main 
1 | 00.00.00 | job1 | 0 
2 | 00.00.00 | job2 | 0 
3 | 00.00.00 | job3 | 0 

数据表：

id | dateTime | jobName | is_main 
1 | 00.00.00 | job1 | 1 
2 | 00.00.00 | ---  | 1 

输出是这样的：

job1 //this is not okay, because of duplicate job1 
job1 
job2 
job3 
_____ 
--- //this is perfect, because I want empty cell to show on top 
job1 
job2 
job3 

Answer 1

SELECT dateTime, id, jobName, max(is_main) from 
(SELECT 
    b.dateTime, 
    a.id, 
    a.jobName, 
    a.is_main 
FROM job_data a, data b 
WHERE a.userEmail = b.userEmail AND a.userEmail = :email 
UNION 
SELECT 
    b.dateTime, 
    b.id, 
    b.jobName, 
    b.is_main 
FROM job_data a, data b 
WHERE a.userEmail = b.userEmail AND a.userEmail = :email 

) 
GROUP BY id