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?STDDEV_SAMP? 函數(shù)計(jì)算樣本標(biāo)準(zhǔn)差。?STDDEV_SAMP? 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 的不同之處在于，?STDDEV? 只有一行輸入數(shù)據(jù)時(shí)返回 0，而 ?STDDEV_SAMP? 返回 NULL。
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說明
樣本標(biāo)準(zhǔn)差是樣本方差的算術(shù)平方根。
語法
STDDEV_SAMP([ALL] expr) [ OVER (analytic_clause) ]作為分析函數(shù)使用時(shí)，您需要使用窗口函數(shù)的完整語法，它對(duì)一組行的集合進(jìn)行計(jì)算并返回多個(gè)值 。作為聚合函數(shù)使用時(shí)，該函數(shù)對(duì)一組行的集合進(jìn)行聚合計(jì)算，結(jié)果只能返回一個(gè)值，此時(shí)不需要加 OVER 關(guān)鍵字。
參數(shù)
|
參數(shù) |
說明 |
|---|---|
|
ALL |
全部數(shù)值列。 |
expr | 是數(shù)值類型（ |
OVER | 使用 |
返回類型
返回類型與參數(shù) ?expr? 的數(shù)據(jù)類型相同。
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 manager_id, last_name, hiredate, salary,STDDEV_SAMP(salary) OVER (PARTITION BY manager_id
ORDER BY hiredate ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) AS cum_sdev
FROM employees ORDER BY manager_id, last_name, hiredate, salary, cum_sdev;返回結(jié)果如下：
+------------+-----------+------------+--------+-------------------------------------------+
| MANAGER_ID | LAST_NAME | HIREDATE | SALARY | CUM_SDEV |
+------------+-----------+------------+--------+-------------------------------------------+
| 100 | De Haan | 2018-05-01 | 11000 | 4702.127178203498995615489088200868644482 |
| 100 | Errazuriz | 2017-07-21 | 1400 | 212.132034355964257320253308631454711785 |
| 100 | Hartstein | 2019-05-01 | 14000 | 6340.346993658943269176828928801701088079 |
| 100 | Partners | 2018-12-01 | 14000 | 6064.899009876421676804205219406952308814 |
| 100 | Raphaely | 2017-07-01 | 1700 | NULL |
| 100 | Raphaely | 2017-07-22 | 1700 | 173.205080756887729352744634150587236694 |
| 100 | Russell | 2019-10-05 | 13000 | 6026.474330580265330900400184969999384459 |
| 100 | Weiss | 2019-07-11 | 13500 | 6244.311697171159907069428668980211861012 |
| 200 | Bell | 2019-05-25 | 13000 | 707.106781186547524400844362104849039285 |
| 200 | Part | 2018-08-11 | 14000 | NULL |
| 200 | Ross | 2019-06-11 | 13500 | 500 |
+------------+-----------+------------+--------+-------------------------------------------+聚合函數(shù)示例
調(diào)用函數(shù)并執(zhí)行以下語句：
SELECT STDDEV_SAMP(salary) FROM employees ;查詢結(jié)果如下：
+-------------------------------------------+
| STDDEV_SAMP(SALARY) |
+-------------------------------------------+
| 5506.194858355615640082358245403620332764 |
+-------------------------------------------+網(wǎng)站標(biāo)題：創(chuàng)新互聯(lián)OceanBase教程：OceanBaseSTDDEV_SAMP
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