字符串：
1.concat對於字符串進行拼接
concat(str1, str2, ..., strN) - Returns the concatenation of str1, str2, ..., strN.
Examples:> SELECT concat('Spark', 'SQL'); SparkSQL
2.concat_ws在拼接的字符串中間添加某種格式
concat_ws(sep, [str | array(str)]+) - Returns the concatenation of the strings separated by sep.
Examples:> SELECT concat_ws(' ', 'Spark', 'SQL'); Spark SQL
3.decode轉碼
decode(bin, charset) - Decodes the first argument using the second argument character set.
Examples: > SELECT decode(encode('abc', 'utf-8'), 'utf-8'); abc
4.encode設置編碼格式
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將每個單詞的首字母變爲大寫，其他字母小寫; lower全部轉爲小寫，upper大寫
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返回字符串的長度
Examples:> SELECT length('Spark SQL '); 10
8.levenshtein編輯距離（將一個字符串變爲另一個字符串的距離）
levenshtein(str1, str2) - Returns the Levenshtein distance between the two given strings.
Examples:> SELECT levenshtein('kitten', 'sitting'); 3
9.lpad返回固定長度的字符串，如果長度不夠，用某種字符補全，rpad右補全
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去除空格或去除開頭的某些字符,rtrim右去除，trim兩邊同時去除
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
11.regexp_extract 正則提取某些字符串，regexp_replace正則替換
Examples:> SELECT regexp_extract('100-200', '(\d+)-(\d+)', 1); 100
Examples: > SELECT regexp_replace('100-200', '(\d+)', 'num'); num-num
12.repeat複製給的字符串n次
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個空格
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('www.apache.org', '.', 2); www.apache
17.translate 替換某些字符串爲
Examples: > SELECT translate('AaBbCc', 'abc', '123'); A1B2C3
18.get_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 SQL
20.to_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}]
時間日期：
一、獲取當前時間
1.current_date獲取當前日期
2018-04-09
2.current_timestamp/now()獲取當前時間
2018-04-09 15:20:49.247
二、從日期時間中提取字段
1.year,month,day/dayofmonth,hour,minute,second
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
4.trunc截取某部分的日期，其他部分默認爲01
第二個參數 ["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將時間轉化爲某種格式的字符串
Examples:> SELECT date_format('2016-04-08', 'y'); 2016
三、日期時間轉換
1.unix_timestamp返回當前時間的unix時間戳
Examples:
> SELECT unix_timestamp(); 1476884637
> SELECT unix_timestamp('2016-04-08', 'yyyy-MM-dd'); 1460041200
2.from_unixtime將時間戳換算成當前時間，to_unix_timestamp將時間轉化爲時間戳
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
3.to_date/date將字符串轉化爲日期格式，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 將1年4等分(range 1 to 4)
Examples:> SELECT quarter('2016-08-31'); 3
四、日期、時間計算
1.months_between兩個日期之間的月數
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返回日期後n個月後的日期
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(減)
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（兩個日期間的天數）
datediff(endDate, startDate) - Returns the number of days from startDate to endDate.
Examples:> SELECT datediff('2009-07-31', '2009-07-30'); 1
6.關於UTC時間
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