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→Perhaps a Simpler Alternative
Aggregate functions in PostgreSQL:
https://www.postgresql.org/docs/9.0/static/functions-aggregate.html
=== Aggregate Functions ===
Table 9-44. Aggregate Functions for Statistics
Function Argument Type Return Type Description
corr(Y, X) double precision double precision correlation coefficient
covar_pop(Y, X) double precision double precision population covariance
covar_samp(Y, X) double precision double precision sample covariance
regr_avgx(Y, X) double precision double precision average of the independent variable (sum(X)/N)
regr_avgy(Y, X) double precision double precision average of the dependent variable (sum(Y)/N)
regr_count(Y, X) double precision bigint number of input rows in which both expressions are nonnull
regr_intercept(Y, X) double precision double precision y-intercept of the least-squares-fit linear equation determined by the (X, Y) pairs
regr_r2(Y, X) double precision double precision square of the correlation coefficient
regr_slope(Y, X) double precision double precision slope of the least-squares-fit linear equation determined by the (X, Y) pairs
regr_sxx(Y, X) double precision double precision sum(X^2) - sum(X)^2/N ("sum of squares" of the independent variable)
regr_sxy(Y, X) double precision double precision sum(X*Y) - sum(X) * sum(Y)/N ("sum of products" of independent times dependent variable)
regr_syy(Y, X) double precision double precision sum(Y^2) - sum(Y)^2/N ("sum of squares" of the dependent variable)
stddev(expression) smallint, int, bigint, real, double precision, or numeric double precision for floating-point arguments, otherwise numeric historical alias for stddev_samp
stddev_pop(expression) smallint, int, bigint, real, double precision, or numeric double precision for floating-point arguments, otherwise numeric population standard deviation of the input values
stddev_samp(expression) smallint, int, bigint, real, double precision, or numeric double precision for floating-point arguments, otherwise numeric sample standard deviation of the input values
variance(expression) smallint, int, bigint, real, double precision, or numeric double precision for floating-point arguments, otherwise numeric historical alias for var_samp
var_pop(expression) smallint, int, bigint, real, double precision, or numeric double precision for floating-point arguments, otherwise numeric population variance of the input values (square of the population standard deviation)
var_samp(expression) smallint, int, bigint, real, double precision, or numeric double precision for floating-point arguments, otherwise numeric sample variance of the input values (square of the sample standard deviation)
==Joe Conway's Documentation on pl/r==
