stddev aggregate function
Applies to: 
Databricks SQL Databricks Runtime
Returns the sample standard deviation calculated from the values in the group. This function is a synonym for std aggregate function.
Syntax
stddev ( [ALL | DISTINCT] expr ) [FILTER ( WHERE cond ) ]
This function can also be invoked as a window function using the OVER clause.
Arguments
expr: An expression that evaluates to a numeric.cond: An optional Boolean expression filtering the rows used for aggregation.
Returns
A DOUBLE.
If DISTINCT is specified the function operates only on a unique set of expr values.
If any group consists of only one row, the function returns NULL for that group.
Examples
SQL
> SELECT stddev(col) FROM VALUES (1), (2), (3), (3) AS tab(col);
0.9574271077563381
> SELECT stddev(DISTINCT col) FROM VALUES (1), (2), (3), (3) AS tab(col);
1.0