Question

我有两个表，一个用户，另一个有错误。他们有2个关系。用户可以修复或提交错误。我想显示带有提交和修复错误的用户名。

我试过这样的事情：

SELECT usr.username, err.description AS ERROR_SOLVED
FROM Users usr, Errors err
WHERE err.solved_by_id=usr.id
UNION 
SELECT usr.username, err.description AS ERROR_SUBMITED
FROM Users usr, Errors err
WHERE err.submited_by_id=usr.id

显然它不起作用，请帮助。

Answer 1

列必须具有相同的描述。

SELECT usr.username, err.description AS ERROR, 1 as SOLVED
FROM Users usr, Errors err
WHERE err.solved_by_id=usr.id
UNION 
SELECT usr.username, err.description AS ERROR, 0 as SOLVED
FROM Users usr, Errors err
WHERE err.submited_by_id=usr.id

会奏效。您还可以定义其他列以显示它的类型。

Answer 2

像这样......

Select usr.username, submittedErrs.description AS ERROR_SUBMITTED, 
   fixedErrs.description AS ERROR_SOLVED
from Users usr
left outer join Errors submittedErrs ON submittedErrs.submitted_by_id=usr.id
left outer join Errors fixedErrs ON fixedErrs.solved_by_id=usr.id

Answer 3

尝试

SELECT usr.username, err.description AS ERROR_SOLVED, 
       err2.description AS ERROR_SUBMITED
FROM Users AS usr 
JOIN Errors AS err ON err.solved_by_id=usr.id
JOIN Errors AS err2 ON err2.submited_by_id=usr.id

Answer 4

在union中使用别名时，第一个查询确定名称。在后续查询中，不可能对同一字段使用其他别名。

然后，您应该添加一个类型字段以区分错误和解决方案。

如果在没有操作类型的情况下将错误/解决方案放在一起就足够了，我建议在on子句中使用OR进行连接：

SELECT
    usr.username,
    err.description
FROM
     Errors err JOIN Users usr ON err.solved_by_id = usr.id OR err.submited_by_id=usr.id

如何选择2个条件分为两列

4 个答案: