How to get the next business date in postgres? - sql

Question

Business days are Monday through Friday.
Given I have a datetime field scheduled_for, how can I find the next business date and return that in a column alias?
I've tried something from another SO answer but it doesn't work as intended.
EXTRACT(ISODOW FROM v.scheduled_for)::integer) % 7 as next_business_day,
Error:
Query 1 ERROR: ERROR: syntax error at or near ")"
LINE 3: EXTRACT(ISODOW FROM v.scheduled_for)::integer % 7) as next...
^
Edit:
Thanks for the suggestions, I've attempted this:
SELECT
v.id AS visit_id,
(IF extract(''dow'' from v.scheduled_for) = 0 THEN
return v.scheduled_for + 1::integer;
ELSIF extract(''dow'' from v.scheduled_for) = 6 THEN
return v.scheduled_for - 1::integer;
ELSE
return v.scheduled_for;
) as next_business_day,
'' as invoice_ref_code,
The error I get is:
Query 1 ERROR: ERROR: syntax error at or near ")"
LINE 1: ) as next_business_day,
^

Answer 1

To generalize you need to create a function to calculate the next business day from a given date.
create or replace function utl_next_business_day(date_in date default current_date)
returns date
language sql immutable leakproof strict
as $$
with cd as (select extract(isodow from date_in)::integer d)
select case when d between 1 and 4
then date_in + 1
else date_in + 1 + (7-d)
end
from cd;
$$;
--- any single date
select current_date, utl_next_business_day();
-- over time span (short)
select gdate::date for_date, utl_next_business_day(gdate::date) next_business_day
from generate_series( current_date, current_date + 14, interval '1 day') gdate;
-- around year end over a time span
with test_date (dt) as
( values (date '2019-12-31')
, (date '2020-12-31'), (date '2021-12-31'),(date '2022-12-31')
, (date '2021-01-01'), (date '2022-01-01'),(date '2023-01-01')
)
select dt, utl_next_business_day(dt) from test_date
order by dt;
Alternatively with the calendar table suggestion from #Eric we get.
-- create and populate work table
create table bus_day_calendar ( bus_day date);
insert into bus_day_calendar (bus_day)
select utl_next_business_day(gdate::date)
from generate_series( date '2018-12-31', date '2023-01-01', interval '1 day') gdate
where extract(isodow from gdate)::integer not in (6,7) ;
--- Function to return next business day
create or replace function utl_next_cal_business_day(date_in date default current_date)
returns date
language sql stable leakproof strict
as $$
select min(bus_day)
from bus_day_calendar
where bus_day > date_in;
$$;
--- any single date
select current_date, utl_next_cal_business_day();
-- over time span (short)
select gdate::date for_date, utl_next_cal_business_day(gdate::date) next_business_day
from generate_series( current_date, current_date + 14, interval '1 day') gdate;
-- around year end over a time span
with test_date (dt) as
( values (date '2019-12-31')
, (date '2020-12-31'), (date '2021-12-31'),(date '2022-12-31')
, (date '2021-01-01'), (date '2022-01-01'),(date '2023-01-01')
)
select dt, utl_next_cal_business_day(dt) from test_date
order by dt;
Neither of these as they currently stand handle a non-business day that falls on Mon-Fri, but both can be modified to do so. Since the calendar table requires only deleting roes I think that becomes the superior method if this is necessary.