检查一个MySql列中是否存在form-posted变量

Question

我有一个发布Class Number值Ex的html表单。 150701-003

在我的php动作文件中，我想检查变量$ class_number是否已经在名为CLASS NO的MySql表列中。

{
        "_id" : ObjectId("5549ec1575bd899c17ec5163"),
        "messages" : [
                 {
                        "subject" : "diohvoidso",
                        "from" : ObjectId("5534a588a12ae5ac11dc6f6b"), //populated
                        "_id" : ObjectId("5549f42c75bd899c17ec5165"),
                        "created" : ISODate("2015-05-06T10:59:56.665Z"),
                        "read" : true,
                        "message" : "icdo ovdw iovhiwiohovhoihreiobv",
                        "participants" : [
                                ObjectId("5530b6208ab0478c2bd23292"),// populated
                         ObjectId("5534a588a12ae5ac11dc6f6b")
                        ]
                }

        ],
        "participants" : [
                ObjectId("5530b6208ab0478c2bd23292"), // logged in user
                ObjectId("5534a588a12ae5ac11dc6f6b")
        ],
        "__v" : 10
}

Answer 1

尝试以下内容：

$result = mysqli_query($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
}

Answer 2

 $check_class_number = mysqli_query($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.";
}

Answer 3

使用mysqli_num_rows属性。

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