Select using ifnull and subquery error SQL Error [1242] [21000]: Subquery returns more than 1 row答案

【问题标题】：Select using ifnull and subquery error SQL Error [1242] [21000]: Subquery returns more than 1 rowSelect using ifnull and subquery error SQL Error [1242] [21000]: Subquery returns more than 1 row
【发布时间】：2021-03-31 02:52:16
【问题描述】：

我想从某个子查询中获取数据，但它只返回 SQL 错误 [1242] [21000]：子查询返回超过 1 行，我的代码有问题吗？

  SELECT
    u.id user_id, p.id user_profileid, p.firstname, p.lastname,
    IFNULL((SELECT SUM(ROUND((DATEDIFF(end_date, start_date) / 365))) FROM employee_experience WHERE user_profileid = p.id GROUP BY user_profileid),0) AS experience,
    (SELECT jobtitle FROM employee_experience WHERE end_date IN (SELECT MAX(end_date) FROM employee_experience GROUP BY user_profileid) AND user_profileid = p.id) AS last_jobtitle,
    IFNULL((SELECT lastsalary FROM employee_experience WHERE end_date IN (SELECT MAX(end_date) FROM employee_experience GROUP BY user_profileid) AND user_profileid = p.id),0) AS last_salary
  FROM
    users u
    LEFT JOIN employee_profile p ON (u.id = p.user_id)
    LEFT JOIN employee_experience e ON (p.id = e.user_profileid)
  WHERE
     (u.roleid = '2') and (u.isverified = '1')
  GROUP BY
    u.id, p.id

【问题讨论】：

标签： mysql subquery

【解决方案1】：

ifnull 仅适用于 1 个值，您的子查询可以返回多个值，要解决此问题，您可以在子查询中使用 limit 1

    SELECT 
           u.id user_id, p.id user_profileid, p.firstname, p.lastname, IFNULL((SELECT
 SUM(ROUND((DATEDIFF(end_date, start_date) / 365))) FROM
 employee_experience WHERE
 user_profileid = p.id GROUP BY
 user_profileid limit 1),0) AS experience,
 (SELECT jobtitle FROM
 employee_experience WHERE end_date
 IN (SELECT MAX(end_date) FROM
 employee_experience GROUP BY
 user_profileid) AND user_profileid =
 p.id) AS last_jobtitle, IFNULL((SELECT
 lastsalary FROM employee_experience
 WHERE end_date IN (SELECT
 MAX(end_date) FROM employee_experience GROUP BY
 user_profileid) AND user_profileid = p.id
 limit 1),0) AS last_salary FROM users u
 LEFT JOIN employee_profile p ON (u.id =
 p.user_id) LEFT JOIN employee_experience e ON (p.id =
 e.user_profileid) 
WHERE 
     (u.roleid = '2')
 and (u.isverified = '1') 
GROUP BY u.id, p.id

【讨论】：