Question

用户表：

userid | first_name | last_name | email |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 | userid | connected_with | date

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

我想查询以查找用户标识1的连接。在这1个用户标识与2,3连接，以及4如何找到用户标识1的连接

Answer 1

你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 Active Record

$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();

就像你在评论中所说，你有两个外键userid＆amp; connected_with，您可以使用union来组合查询结果。首先查询您找到Connection.userid=1的连接。第二个查询，您找到Connection.connected_with=1的连接。然后结合两个结果。

请参阅以下代码

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 Active Record

// 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 |
+--------------------------+

查询从名为user和connection的两个表中获取连接列表

1 个答案: