📅 最后修改于: 2020-11-30 04:54:13 🧑 作者: Mango
本章介绍了Hive中可用的内置功能。这些函数除了用途外，看上去与SQL函数非常相似。
Hive支持以下内置功能：
| Return Type | Signature | Description |
|---|---|---|
| BIGINT | round(double a) | It returns the rounded BIGINT value of the double. |
| BIGINT | floor(double a) | It returns the maximum BIGINT value that is equal or less than the double. |
| BIGINT | ceil(double a) | It returns the minimum BIGINT value that is equal or greater than the double. |
| double | rand(), rand(int seed) | It returns a random number that changes from row to row. |
| string | concat(string A, string B,…) | It returns the string resulting from concatenating B after A. |
| string | substr(string A, int start) | It returns the substring of A starting from start position till the end of string A. |
| string | substr(string A, int start, int length) | It returns the substring of A starting from start position with the given length. |
| string | upper(string A) | It returns the string resulting from converting all characters of A to upper case. |
| string | ucase(string A) | Same as above. | string | lower(string A) | It returns the string resulting from converting all characters of B to lower case. |
| string | lcase(string A) | Same as above. |
| string | trim(string A) | It returns the string resulting from trimming spaces from both ends of A. |
| string | ltrim(string A) | It returns the string resulting from trimming spaces from the beginning (left hand side) of A. |
| string | rtrim(string A) | rtrim(string A) It returns the string resulting from trimming spaces from the end (right hand side) of A. |
| string | regexp_replace(string A, string B, string C) | It returns the string resulting from replacing all substrings in B that match the Java regular expression syntax with C. |
| int | size(Map |
It returns the number of elements in the map type. |
| int | size(Array |
It returns the number of elements in the array type. |
| value of |
cast( |
It converts the results of the expression expr to |
| string | from_unixtime(int unixtime) | convert the number of seconds from Unix epoch (1970-01-01 00:00:00 UTC) to a string representing the timestamp of that moment in the current system time zone in the format of “1970-01-01 00:00:00” |
| string | to_date(string timestamp) | It returns the date part of a timestamp string: to_date(“1970-01-01 00:00:00”) = “1970-01-01” |
| int | year(string date) | It returns the year part of a date or a timestamp string: year(“1970-01-01 00:00:00”) = 1970, year(“1970-01-01”) = 1970 |
| int | month(string date) | It returns the month part of a date or a timestamp string: month(“1970-11-01 00:00:00”) = 11, month(“1970-11-01”) = 11 |
| int | day(string date) | It returns the day part of a date or a timestamp string: day(“1970-11-01 00:00:00”) = 1, day(“1970-11-01”) = 1 |
| string | get_json_object(string json_string, string path) | It extracts json object from a json string based on json path specified, and returns json string of the extracted json object. It returns NULL if the input json string is invalid. |
以下查询演示了一些内置功能：
hive> SELECT round(2.6) from temp;
成功执行查询后，您将看到以下响应：
3.0
hive> SELECT floor(2.6) from temp;
成功执行查询后，您将看到以下响应：
2.0
hive> SELECT ceil(2.6) from temp;
成功执行查询后，您将看到以下响应：
3.0
Hive支持以下内置聚合函数。这些函数的用法与SQL聚合函数相同。
| Return Type | Signature | Description |
|---|---|---|
| BIGINT | count(*), count(expr), | count(*) – Returns the total number of retrieved rows. |
| DOUBLE | sum(col), sum(DISTINCT col) | It returns the sum of the elements in the group or the sum of the distinct values of the column in the group. |
| DOUBLE | avg(col), avg(DISTINCT col) | It returns the average of the elements in the group or the average of the distinct values of the column in the group. |
| DOUBLE | min(col) | It returns the minimum value of the column in the group. |
| DOUBLE | max(col) | It returns the maximum value of the column in the group. |