查看mysql请求是否为空，空集或其中有内容

我想知道如何使用节点JS获取条件，其中mysql Select请求为NULL，空集或其中有内容。

目前我有：

function checkKey(key, cb) {
    var activated = "";
    var sqlcheck = "SELECT activated from authentification where discord_key = ?";
    console.log("in function");
    DB.query(sqlcheck, [key], function (err, result) {
        if (err) throw (err);
        if (result[0] && result[0].activated) {
            activated = result[0].activated;
            console.log("filled key");
        } else {
            activated = false;
            console.log("empty key");
        }
        cb(activatedkey(activated));
        //return (activatedkey(activated));
    })
}

有了这个，我只得到空和空的东西。我正在寻找一种方法来获取EMPTY或NULL或其中的东西。

非常感谢您的帮助

您可以在身份验证表中添加第二行，其中包含最多可能的密钥。因此，您可以使用OR对这两行进行排序，按键将其限制为1。

SELECT activated
FROM authentification
WHERE discord_key = 123456
OR discord_key = 9999999
ORDER BY discord_key LIMIT 1;

样品

    MariaDB [test_arduino]> SELECT * FROM authentification;
    +----+-----------+-------------+
    | id | activated | discord_key |
    +----+-----------+-------------+
    |  1 | 1         | 12345       |
    |  2 | EMPTY     | 9999999     |
    +----+-----------+-------------+
    2 rows in set (0.001 sec)

MariaDB []> SELECT activated
        ->     FROM authentification
        ->     WHERE discord_key = 12345
        ->     OR discord_key = 9999999
        ->     ORDER BY discord_key LIMIT 1;
    +-----------+
    | activated |
    +-----------+
    | 1         |
    +-----------+
    1 row in set (0.001 sec)

    MariaDB []> SELECT activated
        ->     FROM authentification
        ->     WHERE discord_key = 123456
        ->     OR discord_key = 9999999
        ->     ORDER BY discord_key LIMIT 1;
    +-----------+
    | activated |
    +-----------+
    | EMPTY     |
    +-----------+
    1 row in set (0.001 sec)

    MariaDB []>