循环SQL并在PHP中计算sum

我的代码有一个问题。我有两张桌子。第一个employee_id:

| |雇员id

1

2

3

第二个表叫做employee_times:

| Employee_id | Hours_dev | hours_pm |

| 1 | 2 | 3 |

| 1 | 3 | 4 |

| 2 | 3 | 3 |

我要做的是计算每个员工工作的总时间(hours_dev+hours_pm)。例如，employee_id 1已经工作了12小时

到目前为止，我已经尝试从第一个表中检索所有的employee_id，并使用for循环在SQL语句中遍历employee_times(参见下面的代码)。然而，该代码不起作用，因为它对employee_id和total_hours都打印0。

我在本地主机服务器上使用MYSQL。

$sql = "SELECT employee_id FROM employee";$result = mysql_query($sql);While ($row = mysql_fetch_array)｛$employee_id = $row['employee_id'];}

              $employee_id_length = sizeof($employee_id);
              for($i = 0; $i < $employee_id_length; $i++)
              {
                 $sql4 = "SELECT employee_id, hours_dev, hours_pm FROM employee_times WHERE employee_id= '$employee_id[$i]'";
                        $result =  mysql_query($sql4);
                          while($info = mysql_fetch_array($result));
                        {
                            $employee_id = $info['employee_id'];
                            $hours_dev=$info['hours_dev'];
                            $hours_pm=$info['hours_pm'];
                            $total_hours = ($total_hours + $hours_dev + $hours_pm );
                        }
                        //print "$employee_id worked for $total_hours";
              }

 select employee_id, sum(hours_dev)+ sum(hours_pm) as total 
from employee_times WHERE employee_id= '1'
group by employee_id

SELECT
  hours_dev,
  hours_pm,
  sum(hours_dev) + sum(hours_pm) as total_hours
FROM
  employee_times
WHERE
  employee_id = 123
GROUP BY
  employee_id

SELECT Employee_id, SUM(Hours_dev), SUM(Hours_pm), SUM(Hours_dev + Hours_pm) 
FROM employee_times 
GROUP BY Employee_id