Make your own SQL interpreter_PHP tutorial

Make your own SQL interpreter
In some small applications, there is no need to use large database software. If you make your own SQL interpreter, you can manage it using a database.
This interpreter can interpret commonly used SQL commands. You can add other features yourself.

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);
  }

  /**
* Query auxiliary function
*/
  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      $rs[$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        $this->conn[$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("[^ ]([*/>      $search = eregi_replace($regs[1]," $regs[1] ",$search);
    }
    while(eregi("([>      $search = eregi_replace($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      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 = "";

/**Working function for sorting (descending order is called by usort())
*/
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;
}

/**Work function for sorting (ascending order is called by usort())
*/
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;
}
?>

测试例：

<br><?php<br>//require_once "db_text.php";<br><br>$conn = new DB_text;<br>$conn->connect("text1.txt");<br><br>$conn->query("insert into manage (id,title) values (10,'abcd')");<br>$conn->query("insert into manage (id,title) values (2,'43d')");<br>$conn->query("insert into manage (id,title) values (20,'tuu')");<br>$conn->query("update manage set id=101,test='a' where id=10");<br>//$conn->query("delete from manage where id='10'");<br>//$conn->query("delete from manage where id=10 or table='code'");<br><br><br>//$rt = $conn->query("select * from manage where id=101 or table='code' group by 1 order by 1 asc");<br>$rt = $conn->query("select * from manage group by 1 order by id desc");<br><br>print_r($rt);<br><br>?><br>