UNION query with codeigniter's active record pattern

Question

How to do UNION query with PHP CodeIgniter framework's active record query format?

Solution 1

CodeIgniter's ActiveRecord doesn't support UNION, so you would just write your query and use the ActiveRecord's query method.

$this->db->query('SELECT column_name(s) FROM table_name1 UNION SELECT column_name(s) FROM table_name2');

Solution 2

By doing union using last_query(), it may hamper performance of application. Because for single union it would require to execute 3 queries. i.e for "n" union "n+1" queries. It won't much affect for 1-2 query union. But it will give problem if union of many queries or tables having large data.

This link will help you a lot: active record subqueries

We can combine active record with manual queries. Example:

// #1 SubQueries no.1 -------------------------------------------

$this->db->select('title, content, date');
$this->db->from('mytable');
$query = $this->db->get();
$subQuery1 = $this->db->_compile_select();

$this->db->_reset_select();

// #2 SubQueries no.2 -------------------------------------------

$this->db->select('title, content, date');
$this->db->from('mytable2');
$query = $this->db->get();
$subQuery2 = $this->db->_compile_select();

$this->db->_reset_select();

// #3 Union with Simple Manual Queries --------------------------

$this->db->query("select * from ($subQuery1 UNION $subQuery2) as unionTable");

// #3 (alternative) Union with another Active Record ------------

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

Solution 3

This is a quick and dirty method I once used

// Query #1

$this->db->select('title, content, date');
$this->db->from('mytable1');
$query1 = $this->db->get()->result();

// Query #2

$this->db->select('title, content, date');
$this->db->from('mytable2');
$query2 = $this->db->get()->result();

// Merge both query results

$query = array_merge($query1, $query2);

Not my finest work, but it solved my problem.

note: I didn't need to order the result.

Solution 4

You may use the following method to get the SQL statement in the model:

$this->db->select('DISTINCT(user_id)');
$this->db->from('users_master');
$this->db->where('role_id', '1');

$subquery = $this->db->_compile_select();
$this->db->_reset_select();

This way the SQL statement will be in the $subquery variable, without actually executing it.

You have asked this question a long time ago, so maybe you have already got the answer. if not, this process may do the trick.

Solution 5

by modifying somnath huluks answer, i add these following variable and functions to DB_Active_rec class as follows:

class DB_Active_records extends CI_DB_Driver
{

   ....

   var $unions;

   ....

    public function union_push($table = '')
    {
        if ($table != '')
        {
            $this->_track_aliases($table);
            $this->from($table);
        }

        $sql = $this->_compile_select();

        array_push($this->unions, $sql);
        $this->_reset_select();
    }

    public function union_flush()
    {
        $this->unions = array();
    }

    public function union()
    {
        $sql = '('.implode(') union (', $this->unions).')';
        $result = $this->query($sql);
        $this->union_flush();
        return $result;
    }

    public function union_all()
    {
        $sql = '('.implode(') union all (', $this->unions).')';
        $result = $this->query($sql);
        $this->union_flush();
        return $result;
    }
}

therefore you can virtually use unions without dependencies to db_driver.

to use union with this method, you simply make regular active record queries, but calling union_push instead of get.

note: you have to ensure your queries have matching columns like regular unions

example:

    $this->db->select('l.tpid, l.lesson, l.lesson_type, l.content, l.file');
    $this->db->where(array('l.requirement' => 0));
    $this->db->union_push('lessons l');
    $this->db->select('l.tpid, l.lesson, l.lesson_type, l.content, l.file');
    $this->db->from('lessons l');
    $this->db->join('scores s', 'l.requirement = s.lid');
    $this->db->union_push();
    $query = $this->db->union_all();
    return $query->result_array();

would produce:

(SELECT `l`.`tpid`, `l`.`lesson`, `l`.`lesson_type`, `l`.`content`, `l`.`file`
FROM `lessons` l
WHERE `l`.`requirement`=0)
union all 
(SELECT `l`.`tpid`, `l`.`lesson`, `l`.`lesson_type`, `l`.`content`, `l`.`file`
FROM `lessons` l
JOIN `scores` s ON `l`.`requirement`=`s`.`lid`)

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