在mysql中使用limit时计数错误

Question

试图弄清楚为什么这会返回错误的计数......似乎限制对计数没有影响.

例如...如果找到20台计算机,但我将其限制为10(license = 10),我的返回显示20.

$stmt = $db->prepare("
    SELECT count(computer_id)
    FROM computers
    WHERE account_id = :account_id
    ORDER BY computer_id ASC LIMIT 0, :licenses
");

$binding = array(
    'account_id' => $_SESSION['user']['account_id'],
    'licenses' => $_SESSION['user']['licenses']
);
$stmt->execute($binding);

$results = $stmt->fetchAll(PDO::FETCH_COLUMN, 0);

另一方面,这将正确返回10:

$stmt = $db->prepare("
    SELECT computer_id
    FROM computers
    WHERE account_id = :account_id
    ORDER BY computer_id ASC LIMIT 0, :licenses
");

$binding = array(
    'account_id' => $_SESSION['user']['account_id'],
    'licenses' => $_SESSION['user']['licenses']
);
$stmt->execute($binding);

$results = count($stmt->fetchAll(PDO::FETCH_COLUMN, 0));

Answer 1

问题是您的查询结果只有一行,即计算机的总数.添加limit 10将不起作用,因为您没有超过10行,但只有一行.

但是,在第二个查询中,每台计算机只有一行.在这种情况下,limit 10将您的行数限制为10.

你可以做的是这样的事情:

SELECT LEAST(10, count(computer_id))
FROM computers
WHERE account_id = :account_id

如果使用此许可证的计算机少于10台,则结果将小于10;如果至少有10台计算机,则结果将为10.