Getting number of certain days-of-the-week (weekend) from interval in PostgreSQL

Question

Given 2 timestamps in postgres, how do you calculate the time difference without counting whole Saturdays and Sundays?

OR

How do you count the number of Satu

Answer 1

You might find this really helpful:

CREATE OR REPLACE FUNCTION working_days(date, date) RETURNS INT AS
$$
SELECT COUNT(days)::INT
    FROM generate_series($1, $2, '1 day') AS days
    WHERE EXTRACT(DOW FROM days) NOT IN(0, 6);
$$
LANGUAGE 'sql' IMMUTABLE STRICT;

Answer 2

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
$BODY$
        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);
$BODY$
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