summarystats — A composite type returned by the ST_SummaryStats and ST_SummaryStatsAgg functions.
A composite type returned by the ST_SummaryStats and ST_SummaryStatsAgg functions.
count 
                                integer
                            Number of pixels counted for the summary statistics.
sum 
                                double precision
                            Sum of all counted pixel values.
mean 
                                double precision
                            Arithmetic mean of all counted pixel values.
stddev 
                                double precision
                            Standard deviation of all counted pixel values.
min 
                                double precision
                            Minimum value of counted pixel values.
max 
                                double precision
                            Maximum value of counted pixel values.