<?php
/*
	作者：shyhero
	邮箱：shyhero@outlook.com
	Q  Q：1757424878
*/
class DB{
	private $sql = array(
		"field"=>"",
		"where"=>"",
		"order"=>"",
		"limit"=>"",
		"group"=>"",
		"having"=>""
	);
	public function __call($functionName,$arr){     //只有在私有成员数组中存在的键才能被调用
		$functionName = strtolower($functionName);
		if(array_key_exists($functionName,$this -> sql)){
			$this -> sql[$functionName] = $arr[0];
		}else{
			echo "调用的方法不存在";
		}
		return $this;
	}
	public function select(){
		echo "select from {$this -> sql['field']} user {$this -> sql['where']} {$this -> sql['order']} {$this -> sql['limit']} {$this -> sql['group']} {$this -> sql['having']}";
	}
}
$db = new DB();
$db -> field('sex count(sex)')               //只有在私有成员数组中存在的键才能被调用
	-> where('where sex in("m","w")')
	-> group('group by sex')
	-> having('having avg(age) > 25')
	-> select();
$db -> query('d');                           //这个方法不存在就不能调用