The STDDEV (standard deviation) function calculates the square
    root of the variance and is expressed in the same units as the
    source expression.

    Oracle Rdb provides the following statistical functions to
    standard deviation:

    o  STDDEV

       This function calculates the standard deviation.

    o  STDDEV_POP

       This function calculates the standard deviation (the square
       root of the variance) for the population. It is equivalent to
       STDDEV with degrees of freedom fixed at 0, that is, SET FLAGS
       'VARIANCE_DOF(0)' which is the default setting.

    o  STDDEV_SAMP

       This function calculates the standard deviation (the square
       root of the variance) for the subset of sampling of the
       population. It is equivalent to STDDEV with degrees of freedom
       fixed at 1, that is, SET FLAGS 'VARIANCE_DOF(1)' which is the
       default setting. By convention one degree of freedom is used
       when the sampling of the population is performed.