The VARIANCE function calculates the variablity from the mean (or
    average) value.

    Oracle Rdb provides the following variance statistical functions:

    o  VARIANCE

       Calculates the variance of the value set.

    o  VAR_POP

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

    o  VAR_SAMP

       This function calculates the variance for a subset or sampling
       of the population. It is equivalent to VARIANCE with degrees
       of freedom fixed at 1, that is, SET FLAGS 'VARIANCE_DOF(1)'.
       By convention one degree of freedom is used when the sampling
       of the population is performed.