随机数字函数，随机变量函数的期望_好文资源

随机函数 –function to get random number=============================================================– DROP FUNCTION IF EXISTS get_random_number(integer, integer);CREATE OR REPLACE FUNCTION get_random_number(integer, integer) RETURNS integer AS$BODY$DECLARE start_int ALIAS FOR $1; end_int ALIAS FOR $2;BEGIN RETURN trunc(random() * (end_int-start_int + 1) + start_int);END;$BODY$LANGUAGE plpgsql;–产生1-10之间的随机数（包括边缘）–SELECT get_random_number(1, 10); –function for get random date between start_date and end_date– DROP FUNCTION IF EXISTS get_random_date(date, date);CREATE OR REPLACE FUNCTION get_random_date(start_date date, end_date date) RETURNS integer AS$BODY$DECLARE interval_days integer; random_days integer; random_date date;BEGIN interval_days := end_date – start_date; random_days := get_random_number(0, interval_days); random_date := start_date + random_days; RETURN date_part(\’year\’, random_date) * 10000 + date_part(\’month\’, random_date) * 100 + date_part(活动：慈云数据爆款香港服务器，CTG+CN2高速带宽、快速稳定、平均延迟10+ms 速度快，免备案，每月仅需19元！！点击查看\’day\’, random_date);END;$BODY$LANGUAGE plpgsql;– SELECT get_random_date(\’2000-01-01\’, \’2013-12-31\’);–result：201009