PHP新手用的Insert和Update语句构造类

PHP新手用的Insert和Update语句构造类，没多大功能,学习php的朋友可以参考下

使用方法
代码如下:
$mysql = new sqlstr("table1");
$mysql->set("name","value");
$mysql->set("name","1",true);
echo $mysql->insertSql();

代码如下:
class sqlstr
{
private $param=array();
private $tablename;
function sqlstr($tablename)
{
$this->tablename = $tablename;
}
public function set($name,$value,$isnum=false){
$value = str_replace("'","''",$value);
$this->param[$name]=array($value,$isnum);
}
public function insertSql(){
$keys="";
$values="";
foreach($this->param as $key =>$value){
$keys = $keys . $key . ",";
if($value[1]){
$values = $values . $value[0] . ",";
}else{
$values = $values . "'" . $value[0] . "',";
}
}
if($keys!=""){$keys=substr($keys,0,strlen($keys)-1) ;}
if($values!=""){$values=substr($values,0,strlen($values)-1) ;}
return "insert into " .$this->tablename ."($keys) values($values)";
}
public function updateSql($cond){
$group="";
foreach($this->param as $key =>$value){
$group .= $key . "=";
if($value[1]){
$group.= $value[0] . ",";
}else{
$group.= "'" . $value[0] . "',";
}
}
if($group!=""){$group=substr($group,0,strlen($group)-1) ;}
return "update " . $this->tablename ." set $group where " . $cond;
}
}