mysql惯用的日期函数汇总
mysql常用的日期函数汇总 最近做统计时经常用到的几个mysql函数: 1. UNIX_TIMESTAMP()? 该函数返回1970到现在的秒数,括号内也可以带参数,即返回1970年到指定时间段的秒数,注意是秒数,常用java的兄弟们需要注意,因为java中的System.currentTimeMillis()
mysql常用的日期函数汇总最近做统计时经常用到的几个mysql函数:
1. UNIX_TIMESTAMP()?
该函数返回1970到现在的秒数,括号内也可以带参数,即返回1970年到指定时间段的秒数,注意是秒数,常用java的兄弟们需要注意,因为java中的System.currentTimeMillis()返回的是毫秒数
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2. date_format()
举一个例子 date_format(now(), '%Y-%m-%d %H:%i:%s') 将当前时间转换成某种时间格式的字符串,当然now()函数的默认格式已经是 '%Y-%m-%d %H:%i:%s'
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3. FROM_UNIXTIME()
FROM_UNIXTIME(1390357150,'%Y-%m-%d'); 将返回1970年到指定时间段的秒数,转换成固定的时间格式,
这个适用于后台日期存放的是秒数,前台展示时需要的是具体的某种日期的应用
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4. current_date()
这个函数的作用是返回当前的日期,但是这个函数在日期做减法时是会有Bug的,
以今天为例:
select current_date();
2014-01-24 |
我想知道今天以前的30天的日期
select current_date()-30;
20140094 |
显然不是我们想得到的值,经过测试发现当涉及到月份或年份的退位进位时就会出错
对于求今天之前的三十天,可以利用毫秒数做
select FROM_UNIXTIME(UNIX_TIMESTAMP(current_date())-24*60*60*30,'%Y-%m-%d');
哪位大神有更好的方法,欢迎指导
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利用以上函数,就可以做简单的基于在线数量的统计,
相关表
? user_online_count_tbl
相关字段
? user_online_num(当前用户在线数)
? online_statistic_time(统计在线数时的时间)
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5.基于最近10天的平均在线用户数统计
select sum(user_online_num)/count(online_statistic_time) as "avg_online_num", FROM_UNIXTIME(online_statistic_time,'%Y-%m-%d') as "dayTime" from user_online_count_tbl where FROM_UNIXTIME(online_statistic_time,'%Y-%m-%d') = FROM_UNIXTIME(UNIX_TIMESTAMP(current_date())-24*60*60*10,'%Y-%m-%d') group by FROM_UNIXTIME(online_statistic_time,'%Y-%m-%d')
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