kyu5_count_weekdays.sql

-- Count weekdays;
--
-- https://www.codewars.com/kata/58241d05e7a162c5b100010f
--
-- You need to create a function that calculates the number of weekdays (Monday through Friday) between two dates
-- inclusively
--
-- The function should be named weekdays accept two arguments of type DATE and return an INTEGER value:
--      weekdays(DATE, DATE) INTEGER
--
-- The order of arguments shouldn't matter. To illustrate both of the following queries
--      SELECT weekdays('2016-01-01', '2016-01-10');
--      SELECT weekdays('2016-01-10', '2016-01-01');
--
-- should produce the same result:
--      weekdays
--      ---------
--              6
--      (1 row)

CREATE OR REPLACE FUNCTION weekdays(DATE, DATE) RETURNS INTEGER AS
$$
  SELECT COUNT(days)::INTEGER
  FROM generate_series(LEAST($1, $2), GREATEST($1, $2), '1 day') AS days
  WHERE EXTRACT(DOW FROM days) NOT IN (0, 6);
$$
LANGUAGE SQL;