用户24小时按一次按钮?php-mysql

<?php $username = $_SESSION['username']; include('dbcon.php'); if (isset($_POST['req'])) { $query = "SELECT requested FROM users WHERE username='$username' "; $result = mysqli_query($db, $query); $row = mysqli_fetch_array($result); if(empty($row['requested'])) { $request = mysqli_real_escape_string($db, $_POST['request']); $query = "INSERT INTO requests (username, airid) VALUES('$username', '$request')"; mysqli_query($db, $query); $query2 = "UPDATE users SET requested='1' WHERE username='$username'"; mysqli_query($db, $query2); // timer should go here i guess echo '<script>swal({title: "Great!", text: "We will process your request as soon as possible!", type: "success", buttonsStyling: false, heightAuto: false}).then(function(){ location.reload();});</script'; } else { echo '<script>swal({title: "Whoa!", text: "You must wait 48 hours before requesting again!", type: "error", buttonsStyling: false, heightAuto: false}).then(function(){ location.reload();});</script'; } } ?>

DROP TABLE IF EXISTS my_table;

CREATE TABLE my_table 
(id SERIAL PRIMARY KEY
,user_id INT NOT NULL
,dt DATETIME NOT NULL
);

INSERT INTO my_table (user_id,dt) VALUES (101,NOW());
Query OK, 1 row affected (0.00 sec)

SELECT * FROM my_table;
+----+---------+---------------------+
| id | user_id | dt                  |
+----+---------+---------------------+
|  1 |     101 | 2018-10-07 23:21:44 |
+----+---------+---------------------+
1 row in set (0.00 sec)

……大约一分钟后……

INSERT INTO my_table (user_id,dt) 
SELECT 101,NOW() 
  FROM (SELECT 1) x 
  LEFT 
  JOIN my_table y 
    ON y.user_id = 101 
   AND y.dt >= NOW() - INTERVAL 60 SECOND 
 WHERE y.id IS NULL;
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

SELECT * FROM my_table;
+----+---------+---------------------+
| id | user_id | dt                  |
+----+---------+---------------------+
|  1 |     101 | 2018-10-07 23:21:44 |
|  2 |     101 | 2018-10-07 23:23:39 |
+----+---------+---------------------+
2 rows in set (0.00 sec)

……几秒钟后……

INSERT INTO my_table (user_id,dt) 
SELECT 101,NOW() 
  FROM (SELECT 1) x 
  LEFT 
  JOIN my_table y 
    ON y.user_id = 101 
   AND y.dt >= NOW() - INTERVAL 60 SECOND 
 WHERE y.id IS NULL;
Query OK, 0 rows affected (0.00 sec)

SELECT * FROM my_table;
+----+---------+---------------------+
| id | user_id | dt                  |
+----+---------+---------------------+
|  1 |     101 | 2018-10-07 23:21:44 |
|  2 |     101 | 2018-10-07 23:23:39 |
+----+---------+---------------------+
2 rows in set (0.00 sec)