在自己写框架时候会发现，多表查询组装SQL语句 
      1){	$arr = explode(",",$data["1"]);	$length = count($arr);	for($i=0; $i<$length; $i++){		$table .= $pre.$arr[$i].",";	}	$table = substr($table, 0,-1);}else{	$table = $pre.$data["1"];}//条件判断$one = explode(" AND ", $data["2"]);$len1 = count($one);for($i=0; $i<$len1; $i++){	$two[] = explode("=", $one[$i]);}$len2 = count($two);for($i=0; $i<$len2; $i++){	for($j=0; $j<$len2-1; $j++){		if(strpos($two[$i][$j],".") > 1){			$where .= $pre.$two[$i][$j]."=";		}else{			$where .= $two[$i][$j];		}	}}$where = explode("=",$where);$len3 = count($where);for($i=0; $i<$len3; $i++){	if($i%2 == 0){		$c .=$where[$i]."=";	}else{		$c .=$where[$i]." AND ";	}}$where = substr($c, 0,-4);echo $query = "SELECT $filed FROM $table WHERE $where";?>