检查其中一个MySql列中是否存在form-posted变量[关闭]

I have a html form that posts a Class Number value Ex. 150701-003

In my php action file, I want to check if the variable $class_number is already in the MySql table column named CLASS NO.

$class_number = $_POST['class'];
                 echo $class_number;

                  $check_class_number = mysqli_query($con, "SELECT * FROM Academy.COLUMNS 
                  WHERE ClassNumber = '$class_number' ");

                  if(count($check_class_number)>0){
                    echo "exists";
                  }
                  else{
                  echo "It does not exist.";
                  }

 $check_class_number = mysqli_query($con, "SELECT * FROM Academy.COLUMNS 
 WHERE Class_Number = '$class_number' ");

if(count($check_class_number)>0){
    echo "exists";
 //do whatever you want to do
}
else{
  echo "It does not exist.";
}

use the mysqli_num_rows property.

if( $check_class_number->num_rows > 0 ){
//yes
} else {
//no
}

Give the following a try:

$result = mysqli_query($con, "SELECT * FROM Academy.COLUMNS 
                              WHERE ClassNumber = '$class_number'");

if(mysqli_num_rows($result) == 0) {
    // the number does not exist so do whatever you wish
} else {
    // post an error message
}