Make a SQL interpreter by yourself

Make a SQL interpreter by yourself
In some small applications, there is no need to use large database software. You can manage it by making an SQL interpreter by yourself.
This interpreter can explain commonly used SQL commands. You can add other features yourself.

<?php
class DB_text {
  var $conn;
  var $classname = "db_text";
  var $database;
  function on_create() {
  }
  function connect($database_name) {
    $this->database = $database_name;
    if(! file_exists($database_name)) {
      $this->conn = array();
      $this->_close();
    }
    $fp = fopen($this->database,"r");
    $this->conn = unserialize(fread($fp,filesize($this->database)));
    fclose($fp);
  }
  function &query($query) {
    if(eregi("select ",$query)) return $this->_select($query);
    if(eregi("insert ",$query)) return $this->_insert($query);
    if(eregi("delete ",$query)) return $this->_delete($query);
    if(eregi("update ",$query)) return $this->_update($query);
    return array();
  }
  function fetch_row(&$result) {
    if(list($key,$value) = each($result))
      return $value;
    return false;
  }
  function num_rows($result) {
    return count($result);
  }

  /**
* Helper function of query
   */
  function _select($query) {
    if(eregi("(order by (.+))",$query,$regs)) {
      $order = $regs[2];
      $query = eregi_replace($regs[1],"",$query);
    }
    if(eregi("(group by (.+))",$query,$regs)) {
      $group = $regs[2];
      $query = eregi_replace($regs[1],"",$query);
    }
    eregi("select .* from ([0-9a-z_]+) *(where +(.+))?",$query,$regs);
    if($regs[3] != "") {
      $keys = $this->_where($regs[3],"\$this->conn[$regs[1]]");
      while(list($key,$value) = each($keys)) {
        $rs[] = $this->conn[$regs[1]][$value];
      }
    }else {
      $rs = $this->conn[$regs[1]];
    }
    if($order) {
      sscanf($order,"%s %s",$key,$type);
      if(empty($type)) $type = "asc";
        $this->_sort($rs,$key,$type);
    }
    return $rs;
  }
  function _insert($query) {
    eregi("insert +into +([0-9a-z_]+) *(.+) *values? *(.+)",$query,$regs);
    eval("\$key=array$regs[2];");
    eval("\$value=array$regs[3];");
    for($i=0;$i<count($key);$i++)
      $rs[$key[$i]] = $value[$i];
    $this->conn[$regs[1]][] = $rs;
    $this->_close();
  }
  function _update($query) {
    eregi("update +([0-9a-z_]+) +set *(,?.*=.*)+( +where +(.+))",$query,$regs);
    $regs[2] = eregi_replace(",","=",$regs[2]);
    $v = split("=",$regs[2]);
    $keys = $this->_where($regs[4],"\$this->conn[$regs[1]]");
    while(list($key,$value) = each($keys)) {
      for($i=0;$i<count($v);$i+=2)
        $this->conn[$regs[1]][$value][$v[$i]] = eregi_replace("'","",$v[$i+1]);
    }
    $this->_close();
  }
  function _delete($query) {
    eregi("delete +from +([0-9a-z_]+) *(where +(.+))?",$query,$regs);
    $keys = $this->_where($regs[3],"\$this->conn[$regs[1]]");
    while(list($key,$value) = each($keys)) {
      unset($this->conn[$regs[1]][$value]);
    }
    reset($this->conn[$regs[1]]);
    while(list($key,$value) = each($this->conn[$regs[1]])) {
      $ch[] = $value;
    }
    $this->conn[$regs[1]] = $ch;
    $this->_close();
  }
  function _where($search,$table) {
    $search = eregi_replace("\("," ( ",$search);
    $search = eregi_replace("\)"," ) ",$search);
    $search = eregi_replace("\+"," + ",$search);
    $search = eregi_replace("\*"," * ",$search);
    while(eregi("[^ ]([*/><!=-])",$search,$regs)) {
      $search = eregi_replace($regs[1]," $regs[1] ",$search);
    }
    while(eregi("([><!] +=)",$search,$regs)) {
      $search = eregi_replace($regs[1],eregi_replace(" ","",$regs[1]),$search);
    }
    $search = eregi_replace("  "," ",trim($search));
    $search = eregi_replace(" and "," && ",$search);
    $search = eregi_replace(" or "," || ",$search);
    $search = eregi_replace(" = "," == ",$search);
    $ar = split(" ",$search);
    eval("\$t=$table;");

    for($i=0;$i<count($ar);$i++) {
      if(isset($t[0][$ar[$i]]))
        $ar[$i] = "\$value[".$ar][$i]."]";
    }
    $expr = "\$expl=(".join(" ",$ar).");";

    while(list($key,$value) = each($t)) {
      eval($expr);
      if($expl)
        $keys[] = $key;
    }
    return $keys;
  }
  function _sort(&$ar,$key=0,$mode="desc") {
    global $cmp_key;
    $cmp_key = $key;
    if($mode == "asc")
      usort($ar,_cmp_asc);
    else
      usort($ar,_cmp_desc);
  }
  function _close() {
    $fp = fopen($this->database,"w");
    fwrite($fp,serialize($this->conn));
    fclose($fp);
  }
}

/** Sort key
*/
$cmp_key = "";

/** Sorting is done with a working function (called by usort() in descending order)
*/
function _cmp_desc($a,$b) {
  global $cmp_key;
  if ($a[$cmp_key] == $b[$cmp_key]) return 0;
  return ($a[$cmp_key] > $b[$cmp_key]) ? -1 : 1;
}

/** Use working function to sort (called by usort() ascending order)
*/
function _cmp_asc($a,$b) {
  global $cmp_key;
  if ($a[$cmp_key] == $b[$cmp_key]) return 0;
  return ($a[$cmp_key] > $b[$cmp_key]) ? 1 : -1;
}
?>

Test example:
<pre>
<?php
//require_once "db_text.php";

$conn = new DB_text;
$conn->connect("");

$conn->query("insert into manage (id,title) values (10,'abcd')");
$conn->query("insert into manage (id,title) values (2,'43d')");
$conn->query("insert into manage (id,title) values (20,'tuu')");
$conn->query("update manage set id=101,test='a' where id=10");
//$conn->query("delete from manage where id='10'");
//$conn->query("delete from manage where id=10 or table='code'");


//$rt = $conn->query("select * from manage where id=101 or table='code' group by 1 order by 1 asc");
$rt = $conn->query("select * from manage group by 1 order by id desc");

print_r($rt);

?>
</pre>