You don't need PL/pgsql!
You don't need PL/pgsql to create functions that do some pretty sophisticated things. Here's a function written entirely in SQL that returns the inverse cumulative distribution function known in Microsoft Excel™ circles as NORMSINV. CREATE OR REPLACE FUNCTION normsinv(prob float8) RETURNS float8 STRICT LANGUAGE SQL AS $$ WITH constants(a,b,c,d,p_low, p_high) AS ( VALUES( ARRAY[-3.969683028665376e+01::float8 , 2.209460984245205e+02 , -2.759285104469687e+02 , 1.383577518672690e+02 , -3.066479806614716e+01 , 2.506628277459239e+00], ARRAY[-5.447609879822406e+01::float8 , 1.615858368580409e+02 , -1.556989798598866e+02 , 6.680131188771972e+01 , -1.328068155288572e+01], ARRAY[-7.784894002430293e-03::float8 , -3.223964580411365e-01 , -2.400758277161838e+00 , -2.549732539343734e+00 , 4.374664141464968e+00 , 2.938163982698783e+00], ARRAY[7.784695709041462e-03::float8 , 3.224671290700398e-01 , 2.445134137142996e+00 , 3.754408661907416e+00],