查询从名为user和connection的两个表中获取连接列表

Question

User table:

userid | first_name | last_name |email |Password

1    | Tom        | cruise    |[e-mail] |d41d8cd98f00b204e9800998ecf8427e
2    | Tamera     | Manzer    |[e-mail]|d41d8cd98f00b204e9800998ecf8427e
3    | Vergie     | Manzer    |[e-mail] |d41d8cd98f00b204e9800998ecf8427e
4    | Elmo       | Milano    |[e-mail] |d41d8cd98f00b204e9800998ecf8427e

Connection Table

con_id | userid | connected_with |date

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

I want to make query to find connection of userid 1. In this 1 userid is connected with 2, 3, and also 4 so how can I find connection of userid 1

Answer 1

You can get your answer from here.

Read here

MySql Query.

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(); 

Like you said in comment, you have two foreign keys userid & connected_with, you can use union to combine both query result. First query you find the connection where Connection.userid=1. Second query you find the connection where Connection.connected_with=1. Then combine both result.

See the code below

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();

Output

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