SparkSql常见内置函数
字符串：
concat(str1, str2, ..., strN) - Returns the concatenation of str1, str2, ..., strN.
Examples:> SELECT concat('Spark', 'SQL');  SparkSQL
concat_ws(sep, [str | array(str)]+) - Returns the concatenation of the strings separated by sep.
Examples:> SELECT concat_ws(' ', 'Spark', 'SQL');  Spark SQL
datediff是字符型函数3.decode转码
decode(bin, charset) - Decodes the first argument using the second argument character set.
Examples: > SELECT decode(encode('abc', 'utf-8'), 'utf-8');  abc
encode(str, charset) - Encodes the first argument using the second argument character set.
Examples: > SELECT encode('abc', 'utf-8');abc
5.format_string/printf 格式化字符串
format_string(strfmt, obj, ...) - Returns a formatted string from printf-style format strings.
Examples:> SELECT format_string("Hello World %d %s", 100, "days");  Hello World 100 days
6.initcap将每个单词的⾸字母变为⼤写，其他字母⼩写; lower全部转为⼩写，upper⼤写
initcap(str) - Returns str with the first letter of each word in uppercase. All other letters are in lowercase. Words are delimited by white space.
Examples:> SELECT initcap('sPark sql');  Spark Sql
7.length返回字符串的长度
Examples:> SELECT length('Spark SQL ');  10
8.levenshtein编辑距离（将⼀个字符串变为另⼀个字符串的距离）
levenshtein(str1, str2) - Returns the Levenshtein distance between the two given strings.
Examples:> SELECT levenshtein('kitten', 'sitting');  3
9.lpad返回固定长度的字符串，如果长度不够，⽤某种字符补全，rpad右补全
lpad(str, len, pad) - Returns str, left-padded with pad to a length of len. If str is longer than len, the return value is shortened to len characters.
Examples:> SELECT lpad('hi', 5, '??');  hi
10.ltrim去除空格或去除开头的某些字符,rtrim右去除，trim两边同时去除
ltrim(str) - Removes the leading space characters from str.
ltrim(trimStr, str) - Removes the leading string contains the characters from the trim string
Examples:
> SELECT ltrim('    SparkSQL  ');  SparkSQL
> SELECT ltrim('Sp', 'SSparkSQLS');  arkSQLS
Examples: > SELECT regexp_replace('100-200', '(\d+)', 'num');  　num-num
Examples: > SELECT repeat('123', 2);  123123
13.instr返回截取字符串的位置/locate
instr(str, substr) - Returns the (1-based) index of the first occurrence of substr in str. Examples:> SELECT instr('SparkSQL', 'SQL');  6
Examples:> SELECT locate('bar', 'foobarbar');  4
14.space 在字符串前⾯加n个空格
space(n) - Returns a string consisting of n spaces.
Examples:> SELECT concat(space(2), '1');  1
15.split以某些字符拆分字符串
split(str, regex) - Splits str around occurrences that match regex.
Examples:> SELECT split('oneAtwoBthreeC', '[ABC]');      ["one","two","three",""] 16.substr截取字符串，substring_index
Examples:
> SELECT substr('Spark SQL', 5);  k SQL
> SELECT substr('Spark SQL', -3);  SQL
> SELECT substr('Spark SQL', 5, 1);  k
> SELECT substring_index('', '.', 2);  www.apache
Examples: > SELECT translate('AaBbCc', 'abc', '123');  A1B2C3
<_json_object
get_json_object(json_txt, path) - Extracts a json object from path.
Examples:> SELECT get_json_object('{"a":"b"}', '$.a');  b
19.unhex
unhex(expr) - Converts hexadecimal expr to binary.
Examples:> SELECT decode(unhex('537061726B2053514C'), 'UTF-8');  Spark _json
to_json(expr[, options]) - Returns a json string with a given struct value
Examples:
> SELECT to_json(named_struct('a', 1, 'b', 2));  {"a":1,"b":2}
> SELECT to_json(named_struct('time', to_timestamp('2015-08-26', 'yyyy-MM-dd')), map('timestampFormat', 'dd/MM/yyyy'));  {"time":"26/08/2015"}
> SELECT to_json(array(named_struct('a', 1, 'b', 2));  [{"a":1,"b":2}]
> SELECT to_json(map('a', named_struct('b', 1)));  {"a":{"b":1}}
> SELECT to_json(map(named_struct('a', 1),named_struct('b', 2)));  {"[1]":{"b":2}}
> SELECT to_json(map('a', 1));  {"a":1}
> SELECT to_json(array((map('a', 1))));  [{"a":1}]
时间⽇期：
⼀、获取当前时间
1.current_date获取当前⽇期
2018-04-09
2.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
Examples:> SELECT day('2009-07-30'); 30
2.dayofweek (1 = Sunday, 2 = Monday, ..., 7 = Saturday),dayofyear
Examples:> SELECT dayofweek('2009-07-30');  5
Since: 2.3.0
3.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
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
5.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
Since: 2.3.0
6.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
三、⽇期时间转换
1.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
2.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
<_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
4.quarter 将1年4等分(range 1 to 4)
Examples:> SELECT quarter('2016-08-31');  3
四、⽇期、时间计算
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
2. 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
3.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
4.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
5.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
6.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 15:00:0
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

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