MySQL DATEDIFF() 参数问题
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DATEDIFF() Parameter Issue
提问by pcort
The old DATEDIFF() allowed users to use 3 parameters, and I was trying to do this so I could get hours out of my DATEDIFF rather than days, (I'm trying to show hours since a post). In my database I'm using a TIMESTAMP and this line of code to pull a value, and obviously it doesn't work because I have the extra parameter. Once I remove the 'hour' or 'hh' the query runs and returns a value in days.
旧的 DATEDIFF() 允许用户使用 3 个参数，我试图这样做，这样我就可以从 DATEDIFF 中获得数小时而不是数天，（我试图显示自发布以来的时间）。在我的数据库中，我使用 TIMESTAMP 和这行代码来提取一个值，显然它不起作用，因为我有额外的参数。一旦我删除了“小时”或“hh”，查询就会运行并以天为单位返回一个值。
SELECT DATEDIFF(hour, CURDATE(), (SELECT Post_Date FROM Post_T WHERE pk_PostID = 1) )
SELECT DATEDIFF(hour, CURDATE(), (SELECT Post_Date FROM Post_T WHERE pk_PostID = 1) )
Is there an easy way I can return the hourly value?
有没有一种简单的方法可以返回小时值？
Also I'm using MYSQL Version 5.5.20.
另外我使用的是 MYSQL 版本 5.5.20。
回答by Filipe Silva
Like it says in the documentation:
就像它在文档中所说的那样：
DATEDIFF(expr1,expr2)
DATEDIFF() returns expr1 – expr2 expressed as a value in daysfrom one date to the other. expr1 and expr2 are date or date-and-time expressions. Only the date parts of the values are used in the calculation.
DATEDIFF(expr1,expr2)
DATEDIFF() 返回 expr1 – expr2 表示为从一个日期到另一个日期的天数。expr1 和 expr2 是日期或日期和时间表达式。计算中仅使用值的日期部分。
If you want the result in hours you should use Timestampdiff
如果你想以小时为单位的结果，你应该使用Timestampdiff
TIMESTAMPDIFF(unit,datetime_expr1,datetime_expr2)
Returns datetime_expr2 – datetime_expr1, where datetime_expr1 and datetime_expr2 are date or datetime expressions. One expression may be a date and the other a datetime; a date value is treated as a datetime having the time part '00:00:00' where necessary. The unit for the result (an integer) is given by the unit argument.
TIMESTAMPDIFF(unit,datetime_expr1,datetime_expr2)
返回 datetime_expr2 – datetime_expr1，其中 datetime_expr1 和 datetime_expr2 是日期或日期时间表达式。一个表达式可能是日期，另一个表达式可能是日期时间；日期值被视为在必要时具有时间部分“00:00:00”的日期时间。结果的单位（整数）由 unit 参数给出。
The unit argument can be: MICROSECOND (microseconds), SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.
单位参数可以是： MICROSECOND (microseconds), SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.
In your case you can do:
在你的情况下，你可以这样做：
SELECT TIMESTAMPDIFF(hour, CURDATE(), (SELECT Post_Date FROM Post_T WHERE pk_PostID = 1) )
