# STDDEV

`STDDEV(x)` returns standard deviation of x. Standard deviation is defined as the square root of the variance. `STDDEV` operates on a group of rows and return one row of output. Null values are ignored by `STDDEV` function. You can use the `DISTINCT` keyword to exclude duplicate entries.

``````
CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
ENAME VARCHAR2(10),
JOB VARCHAR2(9),
SAL NUMBER(7, 2),
DEPTNO NUMBER(2));

INSERT INTO EMP VALUES (1, 'SMITH', 'CLERK',     800,    20);
INSERT INTO EMP VALUES (2, 'ALLEN', 'SALESMAN', 1600,    30);
INSERT INTO EMP VALUES (3, 'WARD',  'SALESMAN', 1250,    30);
INSERT INTO EMP VALUES (4, 'JONES', 'MANAGER',  2975,    20);
INSERT INTO EMP VALUES (5, 'MARTIN','SALESMAN', 1250,    30);
INSERT INTO EMP VALUES (6, 'BLAKE', 'MANAGER',  2850,    30);
INSERT INTO EMP VALUES (7, 'CLARK', 'MANAGER',  2850,    10);
INSERT INTO EMP VALUES (8, 'SCOTT', 'ANALYST',  3000,    20);
INSERT INTO EMP VALUES (9, 'KING',  'PRESIDENT',3000,    10);
INSERT INTO EMP VALUES (10,'TURNER','SALESMAN', 1500,    30);
INSERT INTO EMP VALUES (11,'ADAMS', 'CLERK',    1500,    20);

SQL> select stddev(sal) from emp;

STDDEV(SAL)
-----------
871.238669

SQL>
``````

Using the `STDDEV` function with the `group by` clause:

``````
SQL> select deptno, stddev(sal) from emp group by deptno;

DEPTNO STDDEV(SAL)
---------- -----------
30  666.520817
20  1098.74455
10  106.066017

SQL>
``````
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