如何限制最多20个用户选择一个包

Question

这是我的代码，负责将选择的每个包名称分配给它特定用户名我的想法是添加另一个查询，例如 query = select 来自username = 'package_name' 的userName；如果受影响的行是 => 20 用户不应该能够执行此查询选择这个包否则 userName 将分配给该包名称

<?php
include("session.php");
include("connection.php");

$Pname= filter_input(INPUT_GET,'Pname');
$user_select = $_SESSION['login_user'];

$query='update users set package_name=? where userName=?';
  
$stmt=mysqli_stmt_init($conn);

mysqli_stmt_prepare($stmt,$query) or exit('Query Error.'. mysqli_stmt_errno($stmt));

@mysqli_stmt_bind_param($stmt,'ss',$Pname,$user_select) or exit('Bind Param Error.'); 

mysqli_stmt_execute($stmt) or exit('Query Execution failed.'. mysqli_stmt_errno($stmt));


if (mysqli_stmt_affected_rows($stmt)>0) echo "package chose successfully.";

mysqli_stmt_close($stmt);


mysqli_close($conn);
?>

Answer 1

使用触发器：

CREATE TRIGGER tr_bi_users
BEFORE INSERT ON users
FOR EACH ROW
BEGIN 
    IF 20 <= (SELECT COUNT(*)
              FROM users
              WHERE package_name = NEW.package_name
                AND userName <> NEW.userName) THEN
        SIGNAL SQLSTATE = '45000'
            SET MESSAGE_TEXT = 'The limit for this package reached.';
    END IF;
END

和更新前的相同触发器。

如何限制最多20个用户选择一个包

how to make a limit 20 users maximum to choose one package

html

php

mysql

mysqli