An enhanced version of the standard function for standard deviation is supported, generating either STDDEV_SAMP (expression) for the sample standard deviation or STDDEV_POP (expression) for the population standard deviation, while returning a value of type float. When dragging a Standard Deviation into a variable, the following tree element is created.
Columns and/or other non-aggregate expressions can be moved over the (empty) branch of the tree.
The enhancement consists of the ability to compute the standard deviation of a date expression, generating for the sample version STDDEV_SAMP (date expression - DATE '1900-01-01').
The standard option to compute the standard deviation over distinct values only is also provided, resulting in the generation for the sample version of STDDEV_SAMP(DISTINCT expression). Both this option as well as the options for population and sample versions of standard deviation are enabled through the Properties panel. Double-click on Standard Deviation, or highlight it and click Properties.