Random string function for PL/Lua

random_string.lua

CREATE OR REPLACE FUNCTION random_string_pllua(string_length INTEGER, lowercase BOOLEAN DEFAULT false) RETURNS text
LANGUAGE pllua VOLATILE
AS $$
	-- math.randomseed(socket.gettime()) -- seems to be needed by luajit only
	local alnum  = {
	'0','1','2','3','4','5','6','7','8','9',
	'a','b','c','d','e','f','g','h','i','j','k','l','m',
	'n','o','p','q','r','s','t','u','v','w','x','y','z',
	'A','B','C','D','E','F','G','H','I','J','K','L','M',
	'N','O','P','Q','R','S','T','U','V','W','X','Y','Z'
	}
	local alnumlen = #alnum
	local output = {}
	local rand = math.random
	if lowercase then
		alnumlen = alnumlen - 26
	end
	local pos = rand(1, alnumlen - 10) + 10
	table.insert(output, alnum[pos])
	if (string_length > 1) then
		for i = 2, string_length do
			pos = rand(1, alnumlen)
			table.insert(output, alnum[pos])
		end
	end
	output = table.concat(output)
	return output
$$;