MySQL STDDEV_SAMP() Function

The MySQL STDDEV_SAMP() function calculates the sample standard deviation of all non-null input values and returns the result.

`STDDEV_SAMP()` Syntax

Here is the syntax for MySQL STDDEV_SAMP() function:

STDDEV_SAMP(expr)

We usually use the STDDEV_SAMP() function like this:

SELECT STDDEV_SAMP(expr), ...
FROM table_name
[WHERE ...];

Or use the STDDEV_SAMP() function with the GROUP BY clause:

SELECT STDDEV_SAMP(expr), group_expr1, group_expr2, ...
FROM table_name
[WHERE ...]
GROUP BY group_expr1, group_expr2, ...;

expr: Required. A column name or expression. It accepts a numeric or binary value.

The MySQL STDDEV_SAMP() function returns the sample standard deviation of all non-null input values .

Note that the STDDEV_SAMP() function only handles non-null values. That is, null values are ignored by the STDDEV_SAMP() function.

If all input values are null, the function will return NULL.

To demonstrate usages of the MySQL BIT_AND() function, we simulate a temporary table using the following statement and UNION and SELECT:

SELECT 4 x
UNION
SELECT 5 x
UNION
SELECT 6 x;

+---+
| x |
+---+
| 4 |
| 5 |
| 6 |
+---+
3 rows in set (0.00 sec)

The following statement uses the STDDEV_SAMP() function to calculate the sample standard deviation of all the values in the x column:

SELECT STDDEV_SAMP(x)
FROM (
    SELECT 4 x
    UNION
    SELECT 5 x
    UNION
    SELECT 6 x
  ) t;

+----------------+
| STDDEV_SAMP(x) |
+----------------+
|              1 |
+----------------+