How to divide a period in columns - postgresql

Question

I am trying to create a query where the first column shows the list of the companies and the other 3 columns their revenues per month. This is what I do:
WITH time_frame AS
(SELECT date_trunc('month',NOW())-interval '0 week'),
time_frame1 AS
(SELECT date_trunc('month',NOW())-interval '1 month'),
time_frame2 AS
(SELECT date_trunc('month',NOW())-interval '2 month')
select table1.company_name,
(CASE
WHEN table2.date_of_transaction = (SELECT * FROM time_frame2) THEN sum(table2.amount)
ELSE NULL
END) AS "current week - 2",
(CASE
WHEN table2.date_of_transaction = (SELECT * FROM time_frame1) THEN sum(table2.amount)
ELSE NULL
END) AS "current week - 1",
(CASE
WHEN table2.date_of_transaction = (SELECT * FROM time_frame2) THEN
sum(table2.amount)
ELSE NULL
END) AS "current week - 2"
from table1
join table2 on table2.table1_id = table.id
where table1.company_joined >= '04-20-2019'
group by 1
When I execute the table this comes out: Error running query: column "table2.date_of_transaction" must appear in the GROUP BY clause or be used in an aggregate function LINE 15: WHEN table2.date_of_transaction = (SELECT * FROM time_frame) TH... ^
Do you have any ideas on how to solve it? Thank you.
company name
month1
month2
name 1
£233
£343
name 2
£243
£34
name 3
£133
£43

Answer 1

you can simplify the statement by using the filter() operator
select t1.company_name,
sum(t2.amount) filter (where t2.date_of_transaction = date_trunc('month',NOW())-interval '2 month'),
sum(t2.amount) filter (where t2.date_of_transaction = date_trunc('month',NOW())-interval '1 month'),
sum(t2.amount) filter (where t2.date_of_transaction = date_trunc('month',NOW()))
from table1 t1
join table2 t2 on t2.table1_id = t1.id
where t1.company_joined >= date '2019-04-20'
group by t1.company_name;
If you really want to put the date ranges into a CTE, you only need one:
with dates (r1, r2, r3) as (
values
(date_trunc('month',NOW())-interval '2 month',
date_trunc('month',NOW())-interval '1 month',
date_trunc('month',NOW()))
)
select t1.company_name,
sum(t2.amount) filter (where t2.date_of_transaction = d.r1),
sum(t2.amount) filter (where t2.date_of_transaction = d.r2),
sum(t2.amount) filter (where t2.date_of_transaction = d.r3)
from table1 t1
cross join dates d
join table2 t2 on t2.table1_id = t1.id
where t1.company_joined >= date '2019-04-20'
group by t1.company_name
;
The CTE dates returns a single row with three columns and thus the cross join doesn't change the resulting number of rows.