从单个表获取通知并与多个表连接并生成单个数组

Question

我有一张像

这样的表格

并从此表中选择所有通知并加入下面提到的表

1. tbl_notice

2. tbl_task



1. tbl_assignment



我试图从像

这样的表中获取数据

$sql = "select * from(
    (
    SELECT a.refer_id as id ,a.refer_tbl,b.task_name as name FROM tbl_notification as a
    LEFT JOIN tbl_task as b ON (a.refer_id= b.task_id )ORDER BY a.created_date desc
    ) UNION
    (
    SELECT c.refer_id as id ,c.refer_tbl, d.notice_title as name FROM tbl_notification as c
    LEFT JOIN tbl_notice as d ON (c.refer_id = d.notice_id)ORDER BY c.created_date desc
    ) UNION
    ( 
    SELECT e.refer_id as id,e.refer_tbl, f.title as name FROM tbl_notification as e
    LEFT JOIN tbl_assignment as f ON (e.refer_id = f.assignment_id) ORDER BY e.created_date desc
    ))";
   $query= $this->db->query($sql)->get();

结果显示第一个表中的数据连接（如果tbl_task）其他tbl_notice和tbl_assignment详细信息为null结果演示像这样

请帮我纠正这个......

Answer 1

当你需要一个普通的（INNER）JOIN时，你正在执行LEFT（OUTER）JOIN。试试这个：

SELECT a.refer_id as id ,a.refer_tbl,b.task_name as name FROM tbl_notification as a
JOIN tbl_task as b ON (a.refer_id= b.task_id )ORDER BY a.created_date desc
UNION
SELECT c.refer_id as id ,c.refer_tbl, d.notice_title as name FROM tbl_notification as c
JOIN tbl_notice as d ON (c.refer_id = d.notice_id)ORDER BY c.created_date desc
UNION
SELECT e.refer_id as id,e.refer_tbl, f.title as name FROM tbl_notification as e
JOIN tbl_assignment as f ON (e.refer_id = f.assignment_id) ORDER BY e.created_date desc

Answer 2

我得到了以下附加代码的答案

select * from ( SELECT a.refer_id as id ,a.refer_tbl,a.created_date,b.task_name as name FROM tbl_notification as a JOIN tbl_task as b ON (a.refer_id= b.task_id AND a.refer_tbl="tbl_task") 
           UNION SELECT c.refer_id as id ,c.refer_tbl,c.created_date, d.notice_title as name FROM tbl_notification as c JOIN tbl_notice as d ON (c.refer_id = d.notice_id AND c.refer_tbl="tbl_notice")
           UNION SELECT e.refer_id as id,e.refer_tbl,e.created_date, f.title as name FROM tbl_notification as e JOIN tbl_assignment as f ON (e.refer_id = f.assignment_id AND e.refer_tbl="tbl_assignment") ) tbl_notification ORDER BY `tbl_notification`.`created_date` desc

亲自帮助我......