Mysql最小功能
是否有一个预定义的 MySQL 函数返回其参数值的最小值（MINIMUM(1,16) -> 1）？
更具体地说，我的一个 mysql 表中有一个现场时间列。
每个访问者每 30 秒轮询一次我的服务器进行更新：
UPDATE `mytable` SET `lastUpdate` = NOW() WHERE `id` = ?;
但我也想更新 timeOnSite 列，如下所示：
UPDATE `mytable` SET `timeOnSite` = (
`timeOnSite` + MINIMUM(
TIMESTAMPDIFF(SECOND, lastUpdate, NOW()), 30
)
),
`lastUpdate` = NOW() WHERE `id` = ?;
但问题是没有这样的 MINIMUM 函数，而且我在 MySQL 手册中找不到它。
Is there a predefined MySQL function that returns minimum
of its arguments' values (MINIMUM(1,16) -> 1)?
To be more specific, I have a time-on-site column in one of my mysql tables.
Every visitor polls my server every 30 sec making an update:
UPDATE `mytable` SET `lastUpdate` = NOW() WHERE `id` = ?;
but I'd like to update also timeOnSite column like this:
UPDATE `mytable` SET `timeOnSite` = (
`timeOnSite` + MINIMUM(
TIMESTAMPDIFF(SECOND, lastUpdate, NOW()), 30
)
),
`lastUpdate` = NOW() WHERE `id` = ?;
But the problem is that there are no such MINIMUM function, and I failed to find it in MySQL manuals.
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这是因为它被称为
LEAST()以避免与聚合函数MIN()混淆。That's because its called
LEAST()to avoid confusion with the aggregate functionMIN().