Question

我想按日期订购2个表，但问题是sql没有同时订购它们。

这是我的查询：

SELECT users_id,CONCAT_WS(' ', users_fname, users_lname)
 AS full_name, reply_message, concern_message
FROM tbl_usersinfo AS i 
LEFT JOIN tbl_concern AS c
 ON c.student_id = i.users_id
LEFT JOIN tbl_reply_concern AS r 
ON r.student_id = i.users_id 
ORDER BY c.date,r.date

我读到我需要输入ISNULL（c.date，r.date），但它无效。

Answer 1

尝试ifnull或coalesce

SELECT users_id,
       CONCAT_WS(' ', users_fname, users_lname) AS full_name,
       reply_message,
       concern_message
  FROM tbl_usersinfo AS i
  LEFT JOIN tbl_concern AS c
    ON c.student_id = i.users_id
  LEFT JOIN tbl_reply_concern AS r
    ON r.student_id = i.users_id
 ORDER BY ifnull(c.date, r.date)

MySQL的等同于ISNULL（在SQL Server中）是IFNULL。在MySQL中，我相信ISNULL只是测试某事物是否为零，并将其评估为0或1。

按日期排序2张表

1 个答案: