STDDEV_POP (Population Standard Deviation) returns the square root of the population variance (VAR_POP) for <number expression>, evaluated for each row remaining in the group.
STDDEV_POP ( [DISTINCT | ALL] <number-expression> )
where ALL includes (and DISTINCT excludes) duplicate values in the input set. ALL is the default. When the the input set has no non-null data, STDDEV_POP returns NULL.
<<number-expression>> can be any any numeric expression.
You may use STDDEV_SAMP as either an aggregate or an analytic function.