HiveSQL常见函数及使用方法（含代码示例）

HiveSQL（Hive SQL）是Apache Hive所使用的SQL方言，专门用于在Hadoop上进行大规模数据处理。以下是一些常见的HiveSQL函数及其使用方法：

1. 聚合函数

COUNT

统计记录数。

SELECT COUNT(*) FROM employees;

SUM

计算数值列的总和。

SELECT SUM(salary) FROM employees;

AVG

计算数值列的平均值。

SELECT AVG(salary) FROM employees;

MAX

返回数值列的最大值。

SELECT MAX(salary) FROM employees;

MIN

返回数值列的最小值。

SELECT MIN(salary) FROM employees;

2. 字符串函数

CONCAT

连接两个或多个字符串。

SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM employees;

SUBSTR

截取字符串的子串。

SELECT SUBSTR(first_name, 1, 3) AS short_name FROM employees;

LENGTH

返回字符串的长度。

SELECT LENGTH(first_name) AS name_length FROM employees;

UPPER

将字符串转换为大写。

SELECT UPPER(first_name) AS upper_name FROM employees;

LOWER

将字符串转换为小写。

SELECT LOWER(first_name) AS lower_name FROM employees;

3. 数学函数

ABS

返回数值的绝对值。

SELECT ABS(salary) AS abs_salary FROM employees;

CEIL

返回不小于指定数值的最小整数。

SELECT CEIL(salary) AS ceil_salary FROM employees;

FLOOR

返回不大于指定数值的最大整数。

SELECT FLOOR(salary) AS floor_salary FROM employees;

ROUND

将数值四舍五入到指定的小数位数。

SELECT ROUND(salary, 2) AS rounded_salary FROM employees;

4. 日期函数

CURRENT_DATE

返回当前日期。

SELECT CURRENT_DATE AS today FROM employees;

CURRENT_TIMESTAMP

返回当前时间戳。

SELECT CURRENT_TIMESTAMP AS now FROM employees;

DATEDIFF

计算两个日期之间的天数差。

SELECT DATEDIFF('2024-12-31', '2024-01-01') AS days_diff FROM employees;

DATE_ADD

在指定日期上加上指定的天数。

SELECT DATE_ADD('2024-01-01', 10) AS new_date FROM employees;

DATE_SUB

在指定日期上减去指定的天数。

SELECT DATE_SUB('2024-01-01', 10) AS new_date FROM employees;

YEAR, MONTH, DAY

分别提取日期的年份、月份和天。

SELECT YEAR(hire_date) AS hire_year, MONTH(hire_date) AS hire_month, DAY(hire_date) AS hire_day FROM employees;

5. 条件函数

IF

根据条件返回不同的值。

SELECT IF(salary > 5000, 'High', 'Low') AS salary_level FROM employees;

CASE

多条件判断，类似于SQL中的CASE WHEN。

SELECT 
  CASE 
    WHEN salary > 7000 THEN 'Very High'
    WHEN salary > 5000 THEN 'High'
    ELSE 'Low'
  END AS salary_level 
FROM employees;

6. 复杂类型函数

SIZE

返回数组或映射的大小。

SELECT SIZE(skill_set) AS skill_count FROM employees;

MAP_KEYS

返回映射的所有键。

SELECT MAP_KEYS(employee_info) AS keys FROM employees;

MAP_VALUES

返回映射的所有值。

SELECT MAP_VALUES(employee_info) AS values FROM employees;

ARRAY_CONTAINS

检查数组中是否包含指定元素。

SELECT ARRAY_CONTAINS(skill_set, 'Java') AS has_java_skill FROM employees;

7. JSON函数

GET_JSON_OBJECT

从JSON字符串中提取指定的字段。

SELECT GET_JSON_OBJECT(employee_json, '$.name') AS employee_name FROM employees;

JSON_TUPLE

将JSON字符串解析为多个列。

SELECT 
  JSON_TUPLE(employee_json, 'name', 'age', 'department') 
FROM employees;

8. 窗口函数

ROW_NUMBER

为结果集中的每一行分配唯一的行号。

SELECT 
  employee_id, 
  ROW_NUMBER() OVER (PARTITION BY department ORDER BY salary DESC) AS row_num 
FROM employees;

RANK

为结果集中的每一行分配排名，排名相等的行具有相同的排名。

SELECT 
  employee_id, 
  RANK() OVER (PARTITION BY department ORDER BY salary DESC) AS rank 
FROM employees;

DENSE_RANK

为结果集中的每一行分配密集排名，排名相等的行具有相同的排名，但没有空缺排名。

SELECT 
  employee_id, 
  DENSE_RANK() OVER (PARTITION BY department ORDER BY salary DESC) AS dense_rank 
FROM employees;

9. 其他常用函数

COALESCE

返回第一个非NULL的值。

SELECT COALESCE(middle_name, first_name, 'N/A') AS name FROM employees;

NVL

如果第一个参数为NULL，则返回第二个参数，否则返回第一个参数。

SELECT NVL(middle_name, 'N/A') AS middle_name FROM employees;

REGEXP_EXTRACT

使用正则表达式从字符串中提取子字符串。

SELECT REGEXP_EXTRACT(email, '([a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+)', 1) AS email_address FROM employees;

SPLIT

将字符串按指定分隔符分割成数组。

SELECT SPLIT(full_name, ' ') AS name_parts FROM employees;