mysql - 在 MySQL 中使用 UNION 的 ORDER BY 子句出错

Question

我在 MySQL 中有以下查询:

(SELECT ue.id, ue.userid, ue.status, ue.timestart, ue.timeend, e.courseid,
        e.id AS enrolid, ra.roleid
 FROM user_enrolments ue
 JOIN enrol e ON e.id = ue.enrolid
 JOIN course c ON c.id = e.courseid
 JOIN user u ON u.id = ue.userid
 JOIN context ct ON ct.instanceid = c.id
 LEFT JOIN role_assignments ra ON ra.userid = u.id AND 
                               ra.contextid = ct.id AND
                               ra.itemid = e.id
 WHERE e.customint1 = 1 AND u.deleted = 0 AND 
       ct.contextlevel = 50 AND (ue.status = 0 OR ue.status = 1)) 

UNION

(SELECT de.enrolid AS id, de.userid, de.status, de.date_ini, de.date_fin, 
        de.courseid, de.enrolid, de.roleid
 FROM deleted_enrols de
 JOIN user u ON u.id = de.userid
 WHERE userid = ANY (SELECT userid FROM local_users WHERE clientid = 1))

ORDER BY u.firstname, u.lastname, c.fullname LIMIT 0, 100

如果我删除 ORBER BY 和 LIMIT，这个查询工作正常......但 ORDER BY 子句给出错误:

Table 'u' from one of the SELECTs cannot be used in global ORDER clause

如果我删除两个 SELECT 查询的括号，错误是不同的:

Table 'u' from one of the SELECTs cannot be used in field list

我也尝试过使用 UNION ALL，但它也不起作用。

有什么建议或线索吗？预先感谢您的时间...

Answer 1

UNION 的结果不包含表“u”中的任何字段，因此这些结果无法按表“u”字段排序。

您也许可以执行 UNION，然后将结果重新连接到表“u”，然后使用它按表“u”字段对结果进行排序。排序存在类似问题 course.fullname，因此也需要重新加入。

SELECT x.id, x.userid, x.status, x.timestart, x.timeend, x.courseid, x.enrolid, x.roleid
FROM ((SELECT ue.id, ue.userid, ue.status, ue.timestart, ue.timeend, e.courseid,
        e.id AS enrolid, ra.roleid
       FROM user_enrolments ue
         JOIN enrol e ON e.id = ue.enrolid
         JOIN course c ON c.id = e.courseid
         JOIN user u ON u.id = ue.userid
         JOIN context ct ON ct.instanceid = c.id
         LEFT JOIN role_assignments ra ON ra.userid = u.id 
           AND ra.contextid = ct.id 
           AND ra.itemid = e.id
       WHERE e.customint1 = 1 AND u.deleted = 0 
           AND ct.contextlevel = 50 AND (ue.status = 0 OR ue.status = 1)) 
       UNION
       (SELECT de.enrolid AS id, de.userid, de.status, de.date_ini, de.date_fin, 
        de.courseid, de.enrolid, de.roleid
        FROM deleted_enrols de
          JOIN user u ON u.id = de.userid
         WHERE userid = ANY (SELECT userid FROM local_users WHERE clientid = 1))
) x
  JOIN user z ON z.id = x.userid
  JOIN course d ON d.id = x.courseid
ORDER BY z.firstname, z.lastname, d.fullname LIMIT 0, 100