查询从名为 user 和 connection 的两个表中获取连接列表

Question

用户表：

用户名 |名字 |姓氏 |电子邮件 |密码

1    | Tom        | cruise    |tom@gmail.com |d41d8cd98f00b204e9800998ecf8427e
2    | Tamera     | Manzer    |Tame@yahoo.com|d41d8cd98f00b204e9800998ecf8427e
3    | Vergie     | Manzer    |Vere@live.com |d41d8cd98f00b204e9800998ecf8427e
4    | Elmo       | Milano    |elmo@live.com |d41d8cd98f00b204e9800998ecf8427e

连接表

con_id |用户名 | connected_with |日期

1    | 1        | 2    |2015-04-26
2    | 1        | 3    |2015-04-26
3    | 4        | 1    |2015-04-26

我想查询userid 1的连接。在这个1中，userid与2、3和4连接，所以我怎样才能找到userid 1的连接

Answer 1

您可以从这里得到答案。

Read here

MySql 查询。

SELECT Connection.connected_with, Connection.date
FROM Connection
JOIN User ON User.userid = Connection.userid
WHERE Connection.userid =1

Codeigniter 活动记录

$this->db->select('connected_with', 'date');
$this->db->from('Connection');
$this->db->join('User', 'User.userid' = 'Connection.userid');
$this->db->where('userid', 1);
$this->db->get(); 

就像你在评论中说的，你有两个外键userid & connected_with，你可以使用联合来组合两个查询结果。首先查询你找到Connection.userid=1所在的连接。第二个查询你找到Connection.connected_with=1 所在的连接。然后合并两个结果。

请看下面的代码

SELECT Connection.userid AS 'Connection'
FROM Connection
JOIN User ON User.userid = Connection.connected_with
WHERE Connection.connected_with =1
UNION
SELECT Connection.connected_with
FROM Connection
JOIN User ON User.userid = Connection.userid
WHERE Connection.userid =1

Codeigniter 活动记录

// First Query
$this->db->select('connected_with', 'date');
$this->db->from('Connection');
$this->db->join('User', 'User.userid' = 'Connection.userid');
$this->db->where('userid', 1);
$query = $this->db->get(); 
$subQuery1 = $this->db->_compile_select();

$this->db->_reset_select();

// Second Query
$this->db->select('userid', 'date');
$this->db->from('Connection');
$this->db->join('User', 'User.userid' = 'Connection.connected_with);
$this->db->where('connected_with', 1);
$query = $this->db->get(); 
$subQuery2 = $this->db->_compile_select();

$this->db->_reset_select();

// Union
$this->db->from("($subQuery1 UNION $subQuery2)");
$this->db->get();

输出

+--------------------------+
| Connection for User ID 1 |
+--------------------------+
|                        4 |
|                        2 |
|                        3 |
+--------------------------+