php foreach在变量0中添加+ = string

Question

我已经创建了这段代码

       $cities = arrary('city1','city2','city3','city4','city5');

       $query = "SELECT * FROM data_entry WHERE ";

        foreach($cities as $city){

           $query += " AND city = '$city' ";

        }

        echo $query;

此代码打印为零

我想像这样生成$ query输出

  SELECT * FROM data_entry WHERE city = 'city1' AND city = 'city2' .... etc.

Answer 1

$ cities = array('city1','city2','city3','city4','city5');

   $query = "SELECT * FROM data_entry WHERE ";

    foreach($cities as $key => $city){
      if($key ==0){
        $query .= " city = '$city' ";
       }
       else{
       $query .= " AND city = '$city' ";
       }
    }

    echo $query;