preorder traversal nodes are not deleting in codeigniter
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I've following sql query to delete the nodes. 

 

    $sql="LOCK TABLE xp_subunit WRITE; ";
                $sql .= "SELECT @myLeft := ".$_GET['lft'].", @myRight :=  ".$_GET['rgt'].", @myWidth :=  ".$_GET['lft']." - lft + 1
                FROM xp_subunit
                WHERE id =".$_GET['id']."; ";
        
                $sql .= "DELETE FROM xp_subunit WHERE lft BETWEEN @myLeft AND @myRight; ";
        
                $sql .= "UPDATE xp_subunit SET rgt = rgt - @myWidth WHERE rgt > @myRight; ";
                $sql .= "UPDATE xp_subunit SET lft = lft - @myWidth WHERE lft > @myRight; ";
                $sql.="UNLOCK TABLES;";
                
                //echo $sql;
                echo $query = $this->db->query($sql);

I tried this query in phpmyadmin it executes successfully and delete the node as desired. but when I'm converting it to codeigniter code it gives mysql syntax error like:    

    You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DELETE FROM xp_subunit WHERE lft BETWEEN @myLeft AND @myRight;UPDATE xp_subunit ' at line 3
    
    SELECT @myLeft := 1, @myRight := 29, @myWidth := 1 - lft + 1 FROM xp_subunit WHERE id =1; DELETE FROM xp_subunit WHERE lft BETWEEN @myLeft AND @myRight;UPDATE xp_subunit SET rgt = rgt - @myWidth WHERE rgt > @myRight;UPDATE xp_subunit SET lft = lft - @myWidth WHERE lft > @myRight;

Does I'm doing something wrong... thanks in adv.