Replace calculated negative values with 0 in PostgreSQL - postgresql

Question

I have a table my_table:
case_id first_created last_paid submitted_time
3456 2021-01-27 2021-01-29 2021-01-26 21:34:36.566023+00:00
7891 2021-08-02 2021-09-16 2022-10-26 19:49:14.135585+00:00
1245 2021-09-13 None 2022-10-31 02:03:59.620348+00:00
9073 None None 2021-09-12 10:25:30.845687+00:00
6891 2021-08-03 2021-09-17 None
I created 2 new variables:
select *,
first_created-coalesce(submitted_time::date) as create_duration,
last_paid-coalesce(submitted_time::date) as paid_duration
from my_table;
The output:
case_id first_created last_paid submitted_time create_duration paid_duration
3456 2021-01-27 2021-01-29 2021-01-26 21:34:36.566023+00:00 1 3
7891 2021-08-02 2021-09-16 2022-10-26 19:49:14.135585+00:00 -450 -405
1245 2021-09-13 null 2022-10-31 02:03:59.620348+00:00 -412 null
9073 None None 2021-09-12 10:25:30.845687+00:00 null null
6891 2021-08-03 2021-09-17 null null null
My question is how can I replace new variables' value with 0, if it is smaller than 0?
The ideal output should look like:
case_id first_created last_paid submitted_time create_duration paid_duration
3456 2021-01-27 2021-01-29 2021-01-26 21:34:36.566023+00:00 1 3
7891 2021-08-02 2021-09-16 2022-10-26 19:49:14.135585+00:00 0 0
1245 2021-09-13 null 2022-10-31 02:03:59.620348+00:00 0 null
9073 None None 2021-09-12 10:25:30.845687+00:00 null null
6891 2021-08-03 2021-09-17 null null null
My code:
select *,
first_created-coalesce(submitted_time::date) as create_duration,
last_paid-coalesce(submitted_time::date) as paid_duration,
case
when create_duration < 0 THEN 0
else create_duration
end as QuantityText
from my_table

Answer 1

greatest(yourvalue,0)
Given yourvalue lower than 0, 0 will be returned as the greater value:
select *,
greatest(0,first_created-coalesce(submitted_time::date)) as create_duration,
greatest(0,last_paid-coalesce(submitted_time::date)) as paid_duration
from my_table
This will also change null values to 0.
case statement
If you wish to keep the null results, you can resort to a regular case statement. In order to alias your calculation you'll have to put it in a subquery or a cte:
select *,
case when create_duration<0 then 0 else create_duration end as create_duration_0,
case when paid_duration<0 then 0 else paid_duration end as paid_duration_0
from (
select *,
first_created-coalesce(submitted_time::date) as create_duration,
last_paid-coalesce(submitted_time::date) as paid_duration
from my_table ) as subquery;
(n+abs(n))/2
If you sum a number with its absolute value, then divide by two (average them out), you'll get that same number if it was positive, or you'll get zero if it was negative because a negative number will always balance itself out with its absolute value:
(-1+abs(-1))/2 = (-1+1)/2 = 0/2 = 0
( 1+abs( 1))/2 = ( 1+1)/2 = 2/2 = 1
select *,
(create_duration + abs(create_duration)) / 2 as create_duration_0,
(paid_duration + abs(paid_duration) ) / 2 as paid_duration_0
from (
select *,
first_created-coalesce(submitted_time::date) as create_duration,
last_paid-coalesce(submitted_time::date) as paid_duration
from my_table ) as subquery;
Which according to this demo, is slightly faster than case and about as fast as greatest(), without affecting null values.
Note that select * pulls everything from below, so you'll end up seeing create_duration as well as create_duration_0 - you can get rid of it by listing your desired output columns explicitly in the outer query. You can also rewrite it without subquery/cte, repeating the calculation, which will look ugly but in most cases planner will notice the repetition and make evaluate it only once
select *,
case when first_created-coalesce(submitted_time::date) < 0
then 0
else first_created-coalesce(submitted_time::date)
end as create_duration,
(abs(last_paid-coalesce(submitted_time::date))+last_paid-coalesce(submitted_time::date))/2 as paid_duration
from my_table ) as subquery;
or using a scalar subquery
select *,
(select case when a<0 then 0 else a end
from (select first_created-coalesce(submitted_time::date)) as alias(a) )
as create_duration,
(select case when a<0 then 0 else a end
from (select last_paid-coalesce(submitted_time::date)) as alias(a) )
as paid_duration
from my_table ) as subquery;
Neither of which help with anything in this case but are good to know.

Answer 2

If you are planning on attaching your SQL Database to an ASP.NET app, you could create a c# script to query your database, and use the following:
Parameters.AddWithValue(‘Data You want to change’ ‘0’);
However, if your not using your SQL database with a ASP.NET app, this will not work.