Thread

<?php
    
    $channel = 3;
    $field = 'field_id_5';
    
    function implode_r($glue, $pieces)
    {
        $return = "";

        if(!is_array($glue)){
            $glue = array($glue);
        }
        
        $thisLevelGlue = array_shift($glue);

        if(!count($glue)) $glue = array($thisLevelGlue);
        
        if(!is_array($pieces)){
            return (string) $pieces;
        }
        
        foreach($pieces as $sub){
            $return .= implode_r($glue, $sub) . $thisLevelGlue;
        }

        if(count($pieces)) $return = substr($return, 0, strlen($return) -strlen($thisLevelGlue));

        return $return;
    }
    
    $this->EE =& get_instance();
    
    $month_start = mktime(0, 0, 0, date("m")  , 1, date("Y"));;
    $month_end = mktime(0, 0, 0, date("m")+1  , 1, date("Y"));;
    
    $results = $this->EE->db->select('titles.entry_id')
                ->from('exp_channel_titles as titles')
                ->join('exp_channel_data as data', 'titles.entry_id = data.entry_id')
                ->where("$field >= $month_start")
                ->where("$field < $month_end")
                ->where('titles.channel_id',$channel)
                ->get()
                ->result_array();
                        
    $ids = implode_r("|", $results);

?>

{exp:channel:entries 
    channel="data" 
    entry_id="<?php echo $ids; ?>"
    }