I suggest you to create a function for use whenever you want and write less ; )
This code above will create a sql function that count and return the amount of weekend days (Sat, Sun) .
Just the way you will have more flexibility to use this function.
CREATE OR REPLACE FUNCTION <YourSchemaNameOptional>.count_full_weekend_days(date, date)
RETURNS bigint AS
select COUNT(MySerie.*) as Qtde
from (select CURRENT_DATE + i as Date, EXTRACT(DOW FROM CURRENT_DATE + i) as DiaDate
from generate_series(date ($1) - CURRENT_DATE, date ($2) - CURRENT_DATE ) i) as MySerie
WHERE MySerie.DiaDate in (6,0);
LANGUAGE 'SQL' IMMUTABLE STRICT;
After that, you can use the function to return only the number of weekend days in a interval.
Here's the example to use:
SELECT <YourSchemaNameOptional>.count_full_weekend_days('2017-09-11', '2017-09-25') as days; --> RES: 4
This select must return four because the first and the second day are Monday, and we have 2 Saturdays and 2 Sundays between them.
Now, to return only business days (without weekends), as you want, just make a subtraction, like the example below:
SELECT (date '2017-09-25' - date '2017-09-11' ) - <YourSchemaName>.count_full_weekend_days('2017-09-11', '2017-09-25'); --> RES: 14 - 4 = 10