OceanBase STDDEV

?STDDEV? 函數(shù)用于計(jì)算總體標(biāo)準(zhǔn)差。?STDDEV? 函數(shù)將數(shù)值型數(shù)據(jù)作為參數(shù)，返回?cái)?shù)值型數(shù)據(jù)。它與函數(shù) ?STDDEV_SAMP? 的不同之處在于，?STDDEV? 只有一行輸入數(shù)據(jù)時返回 0，而 ?STDDEV_SAMP? 返回 NULL。

OceanBase 中標(biāo)準(zhǔn)差的值是函數(shù) ?VARIANCE? 計(jì)算出的方差的算術(shù)平方根。

語法

STDDEV([ DISTINCT | UNIQUE | ALL ] expr) [ OVER (analytic_clause) ]

作為分析函數(shù)使用時，您需要使用窗口函數(shù)的完整語法，它對一組行的集合進(jìn)行計(jì)算并返回多個值 。作為聚合函數(shù)使用時，該函數(shù)對一組行的集合進(jìn)行聚合計(jì)算，結(jié)果只能返回一個值，此時不需要加 ?OVER? 關(guān)鍵字。

參數(shù)

注意 
如果您指定了 ?DISTINCT? 或 ?UNIQUE? 關(guān)鍵字，則 ?analytic_clause? 中不允許出現(xiàn) ?order_by_clause? 和 ?windowing_clause?。

返回類型

返回 ?NUMBER? 類型數(shù)據(jù)。

示例

分析函數(shù)示例

以下語句創(chuàng)建了表 employees，并向里面插入數(shù)據(jù)

CREATE TABLE employees(manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT);
INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-01', 1700);
INSERT INTO employees VALUES(100, 'De Haan', '2018-05-01',11000);      
INSERT INTO employees VALUES(100, 'Errazuriz', '2017-07-21', 1400);
INSERT INTO employees VALUES(100, 'Hartstein', '2019-05-01',14000);     
INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-22', 1700);
INSERT INTO employees VALUES(100, 'Weiss',  '2019-07-11',13500);     
INSERT INTO employees VALUES(100, 'Russell', '2019-10-05', 13000);
INSERT INTO employees VALUES(100, 'Partners',  '2018-12-01',14000);     
INSERT INTO employees VALUES(200, 'Ross',  '2019-06-11',13500);     
INSERT INTO employees VALUES(200, 'Bell', '2019-05-25', 13000);
INSERT INTO employees VALUES(200, 'Part',  '2018-08-11',14000);  
COMMIT;

調(diào)用函數(shù)并執(zhí)行以下語句：

SELECT last_name, salary, STDDEV(salary) OVER (ORDER BY hiredate) "StdDev"
FROM employees WHERE manager_id = 100 ORDER BY last_name, salary, "StdDev";

查詢結(jié)果如下：

+-----------+--------+-------------------------------------------+
| LAST_NAME | SALARY | StdDev                                    |
+-----------+--------+-------------------------------------------+
| De Haan   |  11000 | 4702.127178203498995615489088200868644482 |
| Errazuriz |   1400 |  212.132034355964257320253308631454711785 |
| Hartstein |  14000 | 6340.346993658943269176828928801701088079 |
| Partners  |  14000 | 6064.899009876421676804205219406952308814 |
| Raphaely  |   1700 |                                         0 |
| Raphaely  |   1700 |  173.205080756887729352744634150587236694 |
| Russell   |  13000 | 6026.474330580265330900400184969999384459 |
| Weiss     |  13500 | 6244.311697171159907069428668980211861012 |
+-----------+--------+-------------------------------------------+

聚合函數(shù)示例

調(diào)用函數(shù)并執(zhí)行以下語句：

SELECT STDDEV(salary) FROM employees WHERE manager_id = 100 ;

查詢結(jié)果如下：

+-------------------------------------------+
| STDDEV(SALARY)                            |
+-------------------------------------------+
| 6026.474330580265330900400184969999384459 |
+-------------------------------------------+