STDDEV_SAMP and STDDEV_POP window functions
The STDDEV_SAMP and STDDEV_POP window functions return the sample and population standard deviation of a set of numeric values (integer, decimal, or floatingpoint). See also STDDEV_SAMP and STDDEV_POP functions.
STDDEV_SAMP and STDDEV are synonyms for the same function.
Syntax
STDDEV_SAMP  STDDEV  STDDEV_POP ( [ ALL ] expression ) OVER ( [ PARTITION BY expr_list ] [ ORDER BY order_list frame_clause ] )
Arguments
 expression

The target column or expression that the function operates on.
 ALL

With the argument ALL, the function retains all duplicate values from the expression. ALL is the default. DISTINCT is not supported.
 OVER

Specifies the window clauses for the aggregation functions. The OVER clause distinguishes window aggregation functions from normal set aggregation functions.
 PARTITION BY expr_list

Defines the window for the function in terms of one or more expressions.
 ORDER BY order_list

Sorts the rows within each partition. If no PARTITION BY is specified, ORDER BY uses the entire table.
 frame_clause

If an ORDER BY clause is used for an aggregate function, an explicit frame clause is required. The frame clause refines the set of rows in a function's window, including or excluding sets of rows within the ordered result. The frame clause consists of the ROWS keyword and associated specifiers. See Window function syntax summary.
Data types
The argument types supported by the STDDEV functions are SMALLINT, INTEGER, BIGINT, NUMERIC, DECIMAL, REAL, and DOUBLE PRECISION.
Regardless of the data type of the expression, the return type of a STDDEV function is a double precision number.
Examples
The following example shows how to use STDDEV_POP and VAR_POP functions as window functions. The query computes the population variance and population standard deviation for PRICEPAID values in the SALES table.
select salesid, dateid, pricepaid, round(stddev_pop(pricepaid) over (order by dateid, salesid rows unbounded preceding)) as stddevpop, round(var_pop(pricepaid) over (order by dateid, salesid rows unbounded preceding)) as varpop from sales order by 2,1; salesid  dateid  pricepaid  stddevpop  varpop ++++ 33095  1827  234.00  0  0 65082  1827  472.00  119  14161 88268  1827  836.00  248  61283 97197  1827  708.00  230  53019 110328  1827  347.00  223  49845 110917  1827  337.00  215  46159 150314  1827  688.00  211  44414 157751  1827  1730.00  447  199679 165890  1827  4192.00  1185  1403323 ...
The sample standard deviation and variance functions can be used in the same way.