Question

<?php include('railways.php')?>
<form action='' method='POST'>
<p>Enter trainid </p>
<input type="text" name="trainid"/>
<input type="submit" name="submit"/>
</form>

<?php
if(isset($_POST['submit'])){
$availableSeatsAC="";
$bookedSeatsAC = "";
$id = $_POST['trainid'];
$query = "UPDATE trainstatus SET ";
$query .= "availableSeatsAC = $availableSeatsAC-1, ";
$query .= "bookedSeatsAC = $bookedSeatsAC+1 ";
$query .= "WHERE trainid = '$id'";
$result = mysqli_query($connection , $query);
if(!$result){
  die('QUERY FAILED'.mysqli_error($connection));
   }
   else{
    echo "CORRECTLY WORKED";

   }
}
?>

在数据库中，AvailableSeatsAC设置为10，bookedSeatsAC设置为0。提供训练对象并单击提交按钮后，查询将运行。它在bookedSeatsAC上增加了一个，使它达到了预期的1个，但显示的可用座位数是-1，而不是9。有什么解决办法？

Answer 1

<?php
if(isset($_POST['submit'])){
$id = $_POST['trainid'];
$query = "UPDATE trainstatus SET ";
$query .= "availableSeatsAC = availableSeatsAC-1, ";
$query .= "bookedSeatsAC = bookedSeatsAC+1 ";
$query .= "WHERE trainid = '$id'";
$result = mysqli_query($connection , $query);
if(!$result){
  die('QUERY FAILED'.mysqli_error($connection));
   }
   else{
    echo "CORRECTLY WORKED";

   }
}
?>

在MySQL中将变量减1

1 个答案: