6.2. 内置函数
本节主要介绍统一SQL支持原生Oracle数据库中的函数
6.2.4. 通用比较函数
6.2.4.1. GREATEST
- 语法
GREATEST(value1, ...)
- 描述
- 返回参数的最大值,和函数 LEAST() 相反
参数解释
参数 |
说明 |
---|---|
value1, … |
参数至少为两个(如果只提供一个参数,则会报错)。如果参数中有 NULL,则该函数返回为 NULL |
示例
-- 转换前Oracle SQL:
SELECT GREATEST(2,1), GREATEST('2',1,0), GREATEST('a','b','c'), GREATEST('a', NULL, 'c'), GREATEST('2023-05-15','2023-09-06') from dual;
-------------+-----------------+---------------------+----------------------+-----------------------------------+
GREATEST(2,1)|GREATEST('2',1,0)|GREATEST('A','B','C')|GREATEST('A',NULL,'C')|GREATEST('2023-05-15','2023-09-06')|
-------------+-----------------+---------------------+----------------------+-----------------------------------+
2|2 |c | |2023-09-06 |
-- 转换后OceanBase-MySQL:
SELECT GREATEST(2, 1),GREATEST('2', 1, 0),GREATEST('a', 'b', 'c'),GREATEST('a', NULL, 'c'),GREATEST('2023-05-15', '2023-09-06') FROM dual;
GREATEST(2, 1)|GREATEST('2', 1, 0)|GREATEST('a', 'b', 'c')|GREATEST('a', NULL, 'c')|GREATEST('2023-05-15', '2023-09-06')|
--------------+-------------------+-----------------------+------------------------+------------------------------------+
2| 2.0|c | |2023-09-06 |
6.2.4.2. LEAST
- 语法
LEAST(value1, ...)
- 描述
- 返回参数的最小值,和 GREATEST() 函数相反
参数解释
参数 |
说明 |
---|---|
value1, … |
参数至少为两个;如果参数中有 NULL,返回值为 NULL |
示例
-- 转换前Oracle SQL:
SELECT LEAST(2, null), LEAST('2',4,9), LEAST('a','b','c'), LEAST('a',NULL,'c'), LEAST('2014-05-15','2014-06-01') FROM dual;
-------------+--------------+------------------+-------------------+--------------------------------+
LEAST(2,NULL)|LEAST('2',4,9)|LEAST('A','B','C')|LEAST('A',NULL,'C')|LEAST('2014-05-15','2014-06-01')|
-------------+--------------+------------------+-------------------+--------------------------------+
|2 |a | |2014-05-15 |
-- 转换后OceanBase-MySQL:
SELECT LEAST(2, NULL),LEAST('2', 4, 9),LEAST('a', 'b', 'c'),LEAST('a', NULL, 'c'),LEAST('2014-05-15', '2014-06-01') FROM dual;
LEAST(2, NULL)|LEAST('2', 4, 9)|LEAST('a', 'b', 'c')|LEAST('a', NULL, 'c')|LEAST('2014-05-15', '2014-06-01')|
--------------+----------------+--------------------+---------------------+---------------------------------+
| 2.0|a | |2014-05-15 |