How to create a pivot table in Postgresql using case when? - postgresql

Question

I want to create a pivot table using postgresql. I could accomplish this using SQLite, and I thought the logic would be similar, but it doesn't seem to be the case.
Here's the sample table:
create table df(
campaign varchar(50),
date date not null,
revenue integer not null
);
insert into df(campaign,date,revenue) values('A','2019-01-01',10000);
insert into df(campaign,date,revenue) values('B','2019-01-02',7000);
insert into df(campaign,date,revenue) values('A','2018-01-01',5000);
insert into df(campaign,date,revenue) values('B','2018-01-01',3500);
here's my sqlite code to transform the tidy data into pivot table:
select
sum(case when strftime('%Y', date) = '2019' then revenue else 0 end) as '2019',
sum(case when strftime('%Y', date) = '2018' then revenue else 0 end) as '2018',
campaign
from df
group by campaign
the result would be like this:
2018 2019 campaign
5000 10000 A
3500 7000 B
I tried making the similar code using postgres, I will just use the year 2019:
select
sum(case when extract('year' from date) = '2019' then revenue else 0 end) as '2019',
campaign
from df
group by campaign
somehow the code doesn't work, I don't understand what's wrong.
Query Error: error: syntax error at or near "'2019'"
what do I miss here?
db-fiddle link:
https://www.db-fiddle.com/f/f1WjMAAxwSPRvB8BrxECN7/0

Answer 1

The function strftime() is used to extract various parts of a date in SQLite, but is not supported by Postgresql.
Use date_part():
select campaign,
sum(case when date_part('year', date) = '2019' then revenue else 0 end) as "2019",
sum(case when date_part('year', date) = '2018' then revenue else 0 end) as "2018"
from df
group by campaign
Or use Postgresql's FILTER clause:
select campaign,
sum(revenue) filter (where date_part('year', date) = '2019') as "2019",
sum(revenue) filter (where date_part('year', date) = '2018') as "2018"
from df
group by campaign
Also, don't use single quotes for table/column names.
SQLite allows it but Postgresql does not.
It accepts only double quotes which is the SQL standard.
See the demo.