## Syntax
```mermaid
%%{init: {
'theme': 'base',
'flowchart': { 'padding': '7', 'nodeSpacing': '20', 'rankSpacing': '20' },
'themeVariables': {
'fontSize': '11px',
'fontFamily': 'Arial'
}
}}%%
flowchart TD
stdDevAggregateFunction_start((START))
stdDevAggregateFunction_start --> stdDevAggregateFunction_0_0[STDDEV]:::quoted
stdDevAggregateFunction_0_0 --> stdDevAggregateFunction_0_1["("]:::quoted
stdDevAggregateFunction_0_1 --> stdDevAggregateFunction_0_2[DISTINCT]:::quoted
stdDevAggregateFunction_0_2 --> stdDevAggregateFunction_0_3[<a href="Invantive UniversalSQL/Grammar/Expression" class="internal-link">expression</a>]
stdDevAggregateFunction_0_3 --> stdDevAggregateFunction_0_4[")"]:::quoted
stdDevAggregateFunction_0_4 --> stdDevAggregateFunction_end((END))
```
## Purpose
Group function to find the standard deviation from a group of numerical values. The population standard deviation is calculated: the sum of the squared deviations from the average is divided by the number of values. The outcome for a group with one single value is 0. With `DISTINCT`, each unique value is included once.
## Examples
The following example calculates the standard deviation of the outstanding balances of the Wholesale customers, for instance to judge how evenly the credit risk is spread within the segment:
```sql
select stddev(cus.balance)
from csvtable
( passing 'Acme Industries#Manufacturing#12500#50000|Bergmann GmbH#Manufacturing#0#25000|Carlson Ltd#Wholesale#2500#10000|Dubois SA#Wholesale#7500#10000|Everest BV#Services##5000'
row delimiter '|'
column delimiter '#'
columns name varchar2 position next
, segment varchar2 position next
, balance number position next
, credit_limit number position next
) cus
where cus.segment = 'Wholesale'
-------------------
2500
```
The following example calculates the standard deviation of the outstanding balances per customer segment, excluding customers without a balance:
```sql
select cus.segment
, stddev(cus.balance)
from csvtable
( passing 'Acme Industries#Manufacturing#12500#50000|Bergmann GmbH#Manufacturing#0#25000|Carlson Ltd#Wholesale#2500#10000|Dubois SA#Wholesale#7500#10000|Everest BV#Services##5000'
row delimiter '|'
column delimiter '#'
columns name varchar2 position next
, segment varchar2 position next
, balance number position next
, credit_limit number position next
) cus
where cus.balance is not null
group
by cus.segment
order
by cus.segment
-------------------
Manufacturing 6250
Wholesale 2500
```