UNION query with codeigniter's active record pattern

How to do UNION query with PHP CodeIg开发者_如何学运维niter framework's active record query format?

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');

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();

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.

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.

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`)

I found this library, which worked nicely for me to add UNION in an ActiveRecord style:

https://github.com/NTICompass/CodeIgniter-Subqueries

BUT I had to grab the get_compiled_select() method from the dev branch of CodeIgniter first (available here: https://github.com/EllisLab/CodeIgniter/blob/develop/system/database/DB_query_builder.php -- DB_query_builder will be replacing DB_active_rec). Presumably this method will be available in a future production release of CodeIgniter.

Once I added that method to DB_active_rec.php in system/database it worked like a charm. (I didn't want to use the dev version of CodeIgniter as this is a production app.)

This is solution I am using:

$union_queries = array();
$tables = array('table1','table2'); //As much as you need
foreach($tables as $table){
    $this->db->select(" {$table}.row1, 
                        {$table}.row2,
                        {$table}.row3");
    $this->db->from($table);
    //I have additional join too (removed from this example)
    $this->db->where('row4',1);
    $union_queries[] = $this->db->get_compiled_select();
}
$union_query = join(' UNION ALL ',$union_queries); // I use UNION ALL
$union_query .= " ORDER BY row1 DESC LIMIT 0,10";
$query = $this->db->query($union_query);

try this one

function get_merged_result($ids){                   
    $this->db->select("column");
    $this->db->distinct();
    $this->db->from("table_name");
    $this->db->where_in("id",$model_ids);
    $this->db->get(); 
    $query1 = $this->db->last_query();

    $this->db->select("column2 as column");
    $this->db->distinct();
    $this->db->from("table_name");
    $this->db->where_in("id",$model_ids);

    $this->db->get(); 
    $query2 =  $this->db->last_query();
    $query = $this->db->query($query1." UNION ".$query2);

    return $query->result();
}

bwisn's answer is better than all and will work but not good in performance because it will execute sub queries first. get_compiled_select does not run query; it just compiles it for later run so is faster try this one

$this->db->select('title, content, date');
$this->db->where('condition',value);
$query1= get_compiled_select("table1",FALSE);
$this->db->reset_query();

$this->db->select('title, content, date');
$this->db->where('condition',value);
$query2= get_compiled_select("table2",FALSE);
$this->db->reset_query();

$query = $this->db->query("$query1 UNION $query2");

Here's a solution I created:

$query1 = $this->db->get('Example_Table1');
$join1 = $this->db->last_query();
$query2 = $this->db->get('Example_Table2');
$join2 = $this->db->last_query();
$union_query = $this->db->query($join1.' UNION '.$join2.' ORDER BY column1,column2);