一、获取当前时间
- current_date获取当前日期
2018-04-09 - current_timestamp/now()获取当前时间
2018-04-09 15:20:49.247
二、从日期时间中提取字段
- year,month,day/dayofmonth,hour,minute,second
Examples:
> SELECT day('2009-07-30');
30`
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- dayofweek (1 = Sunday, 2 = Monday, …, 7 = Saturday),dayofyear
Examples:
> SELECT dayofweek('2009-07-30');
5`
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- weekofyear
weekofyear(date) - Returns the week of the year of the given date. A week is considered to start on a Monday and week 1 is the first week with >3 days.
Examples:
> SELECT weekofyear('2008-02-20');
8`
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- trunc截取某部分的日期，其他部分默认为01
第二个参数 [“year”, “yyyy”, “yy”, “mon”, “month”, “mm”]
Examples:
> SELECT trunc('2009-02-12', 'MM');
2009-02-01
> SELECT trunc('2015-10-27', 'YEAR');
2015-01-01`
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- date_trunc [“YEAR”, “YYYY”, “YY”, “MON”, “MONTH”, “MM”, “DAY”, “DD”, “HOUR”, “MINUTE”, “SECOND”, “WEEK”, “QUARTER”]
Examples:
> SELECT date_trunc('2015-03-05T09:32:05.359', 'HOUR');
2015-03-05T09:00:00`
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- date_format将时间转化为某种格式的字符串
Examples:
> SELECT date_format('2016-04-08', 'y');
2016`
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三、日期时间转换
- unix_timestamp返回当前时间的unix时间戳
Examples:
> SELECT unix_timestamp(); 1476884637
> SELECT unix_timestamp('2016-04-08', 'yyyy-MM-dd'); 1460041200`
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- from_unixtime将时间戳换算成当前时间，to_unix_timestamp将时间转化为时间戳
Examples:
> SELECT from_unixtime(0, 'yyyy-MM-dd HH:mm:ss'); 1970-01-01 00:00:00
> SELECT to_unix_timestamp('2016-04-08', 'yyyy-MM-dd'); 1460041200`
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- to_date/date将字符串转化为日期格式，to_timestamp（Since: 2.2.0）
> SELECT to_date('2009-07-30 04:17:52'); 2009-07-30
> SELECT to_date('2016-12-31', 'yyyy-MM-dd'); 2016-12-31
> SELECT to_timestamp('2016-12-31 00:12:00'); 2016-12-31 00:12:00`
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- quarter 将1年4等分(range 1 to 4)
Examples:
> SELECT quarter('2016-08-31');
3`
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四、日期、时间计算
- months_between两个日期之间的月数
months_between(timestamp1, timestamp2) - Returns number of months between timestamp1 and timestamp2.
Examples:
> SELECT months_between('1997-02-28 10:30:00', '1996-10-30');
3.94959677`
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- add_months返回日期后n个月后的日期
Examples:
> SELECT add_months('2016-08-31', 1);
2016-09-30`
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- last_day(date),next_day(start_date, day_of_week)
Examples:
> SELECT last_day('2009-01-12'); 2009-01-31
> SELECT next_day('2015-01-14', 'TU'); 2015-01-20`
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- date_add,date_sub(减)
date_add(start_date, num_days) - Returns the date that is num_days after start_date.
Examples:
> SELECT date_add('2016-07-30', 1); 2016-07-31`
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- datediff（两个日期间的天数）
datediff(endDate, startDate) - Returns the number of days from startDate to endDate.
Examples:
> SELECT datediff('2009-07-31', '2009-07-30');
1`
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- 关于UTC时间
- to_utc_timestamp
to_utc_timestamp(timestamp, timezone) - Given a timestamp like ‘2017-07-14 02:40:00.0’, interprets it as a time in the given time zone, and renders that time as a timestamp in UTC. For example, ‘GMT+1’ would yield ‘2017-07-14 01:40:00.0’.
Examples:
> SELECT to_utc_timestamp('2016-08-31', 'Asia/Seoul');
2016-08-30 15:00:00`
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- from_utc_timestamp
from_utc_timestamp(timestamp, timezone) - Given a timestamp like ‘2017-07-14 02:40:00.0’, interprets it as a time in UTC, and renders that time as a timestamp in the given time zone. For example, ‘GMT+1’ would yield ‘2017-07-14 03:40:00.0’.
Examples:
> SELECT from_utc_timestamp('2016-08-31', 'Asia/Seoul');
2016-08-31 09:00:00五、Hive常用函数
1.数学函数
round(DOUBLE d) : 返回DOUBLE型的d的BIGINT类型的近似值
round(DOUBLE d，INT) : 返回DOUBLE型的d的保留n位小数的DOUBLE类型的近似值
floor(DOUBLE d): d是DOUBLE类型的，返回<=d的最大的BIGINT值
ceil(DOUBLE d): d是DOUBLE类型的，返回>=d的最小的BIGINT值
rand() rand(INT seed): 每行返回一个DOUBLE型的随机数，整数seed是随机因子
exp(DOUBLE d)：返回e的d幂次方
ln(DOUBLE d): 以自然数为底d的对数
log10(DOUBLE d): 以10为底的d的对数
log2(DOUBLE d): 以2为底的d的对数
log（DOUBLE base,DOUBLE d）以base为底的d的对数
pow(DOUBLE d,DOUBLE p) power(DOUBLE d,DOUBLE p): 计算d的p次幂
sqrt(DOUBLE d): d的平方根
bin(DOUBLE i): 计算二进制值i的STRING类型值
hex(BIGINT i): 计算十六进制值i的STRING类型值
unhex(STRING i)： hex的逆方法
conv(STRING num,INT from_base,INT to_base): 将STRING类型的num 从from_base进制转化为to_base 进制
abs(DOUBLE d): 计算d的绝对值
pmod(INT i1 ,INT i2): i1对i2取模
sin(DOUBLE d): 返回d的正弦值
cos(DOUBLE d): 返回d的余弦值
asin(DOUBLE d): 返回d的反正弦值
acos(DOUBLE d): 返回d的反余弦值
tan(DOUBLE d): 返回d的正切值
atan(DOUBLE d): 返回d的反正切值
degrees(DOUBLE d): 将弧度值d转化为角度值
radians(DOUBLE d): 将角度值d转化为弧度值
positive(DOUBLE d): 返回+d
negative(DOUBLE d): 返回-d
sign(DOUBLE d): 如果d是正数，则返回+1.0，如果d是负数，则返回-1.0，否则为02.日期函数
to_date(string timestamp):返回时间字符串中的日期部分,如to_date('1970-01-01 00:00:00')='1970-01-01'
current_date:返回当前日期
year(date)：返回日期date的年,类型为int如year('2019-01-01')=2019
month(date)：返回日期date的月,类型为int,如month('2019-01-01')=1
day(date): 返回日期date的天,类型为int,如day('2019-01-01')=1
weekofyear(date1)：返回日期date1位于该年第几周。如weekofyear('2019-03-06')=10
datediff(date1,date2):返回日期date1与date2相差的天数，如datediff('2019-03-06','2019-03-05')=1
date_add(date1,int1):返回日期date1加上int1的日期,如date_add('2019-03-06',1)='2019-03-07'
date_sub(date1,int1):返回日期date1减去int1的日期,如date_sub('2019-03-06',1)='2019-03-05'
months_between(date1,date2):返回date1与date2相差月份,如months_between('2019-03-06','2019-01-01')=2
add_months(date1,int1):返回date1加上int1个月的日期，int1可为负数。如add_months('2019-02-11',-1)='2019-01-11'
last_day(date1):返回date1所在月份最后一天。如last_day('2019-02-01')='2019-02-28'
next_day(date1,day1):返回日期date1的下个星期day1的日期。day1为星期X的英文前两字母如next_day('2019-03-06','MO') 返回'2019-03-11'
trunc(date1,string1):返回日期最开始年份或月份。string1可为年(YYYY/YY/YEAR)或月(MONTH/MON/MM)。如trunc('2019-03-06','MM')='2019-03-01'，trunc('2019-03-06','YYYY')='2019-01-01'
unix_timestamp():返回当前时间的unix时间戳，可指定日期格式。如unix_timestamp('2019-03-06','yyyy-mm-dd')=1546704180
from_unixtime():返回unix时间戳的日期，可指定格式。如select from_unixtime(unix_timestamp('2019-03-06','yyyy-mm-dd'),'yyyymmdd')='20190306'3.条件函数
if(boolean,t1,t2):若布尔值成立，则返回t1,反正返回t2。如if(1>2,100,200)返回200
case when boolean then t1 else t2 end:若布尔值成立，则t1,否则t2,可加多重判断
coalesce(v0,v1,v2):返回参数中的第一个非空值,若所有值均为null,则返回null。如coalesce(null,1,2)返回1
isnull(a):若a为null则返回true，否则返回false4.字符串函数
length(string1):返回字符串长度
concat(string1,string2):返回拼接string1及string2后的字符串
concat_ws(sep,string1,string2):返回按指定分隔符拼接的字符串
lower(string1):返回小写字符串，同lcase(string1)。upper()/ucase()：返回大写字符串
trim(string1):去字符串左右空格，ltrim(string1):去字符串左空格。rtrim(string1):去字符串右空格
repeat(string1，int1)：返回重复string1字符串int1次后的字符串
reverse(string1):返回string1反转后的字符串。如reverse('abc')返回'cba'
rpad(string1,len1,pad1):以pad1字符右填充string1字符串，至len1长度。如rpad('abc',5,'1')返回'abc11'。lpad()：左填充
split(string1,pat1):以pat1正则分隔字符串string1,返回数组。如split('a,b,c',',')返回["a","b","c"]
substr(string1,index1,int1):以index位置起截取int1个字符。如substr('abcde',1,2)返回'ab'5.聚合函数
count():统计行数
sum(col1):统计指定列和
avg(col1):统计指定列平均值
min(col1):返回指定列最小值
max(col1):返回指定列最大值6.表生成函数
explode (array):返回多行array中对应的元素。如explode(array('A','B','C'))返回
explode(map):返回多行map键值对对应元素。如explode(map(1,'A',2,'B',3,'C'))返回7.窗口函数
row_number() over(partitiion by .. order by .. ):根据partition排序,相同值取不同序号，不存在序号跳跃
rank() over(partition by .. order by .):根据partition排序，相同值取相同序号，存在序号跳跃
dense_rank() over(partition by .. order by ..):根据partition排序，相同值取相同序号，不存在序号跳跃
sum() over(partition by .. order by ..)
count() over(partition by .. order by ..)
lag(col,n) over(partition by .. order by ..) ：查看当前行的上第n行
lead(col,n) over(partition by .. order by ..)：查看当前行的下第n行
first_value() over(partition by .. order by ..):满足partition及排序的第一个值
last_value() over(partition by .. order by ..):满足partition及排序的最后值
ntile(n) over(partition by .. order by ..):满足partition及排序的数据分成n份
partition内更细的划分，可使用windows子句。常见子句为：
preceding：往前
following：往后
current row：当前行
unbounded：起点，unbounded preceding 表示从前面的起点， unbounded following：表示到后面的终点
使用如：、
sum(col) over(partition by .. order by .. rows between 1 preceding and current row):当前行与前一行做聚合8.行列转换
concat_ws(sep, collect_set(col1)) :同组不同行合并成一列，以sep分隔符分隔。collect_set在无重复的情况下也可以collect_list()代替。collect_set()去重，collect_list()不去重
lateral view explode(split(col1,',')) :同组同列的数据拆分成多行，以sep分隔符区分