How to transpose data in postgresql

Suppose you have a table  tbl_sales as below:

Country	Category	date	sales
USA	FOOD	12/30/2017	1254
USA	FOOD	09/30/2017	1154
USA	FOOD	06/30/2017	1200
USA	FOOD	03/30/2017	1500
USA	TOYS	12/30/2017	1478
USA	TOYS	09/30/2017	5684
USA	TOYS	06/30/2017	4859
USA	TOYS	03/30/2017	1548

and you have to transpose date into columns of 4 quarters.

First create rank function to distinct the quarters from date:

select row_number() over (partition by country, category, sales,
date_part('year', date) order by country, category asc, sales, date desc ) as row_num,* from tbl_sales 

above query will add row_num column as shown below:

row_num	country	category	date	sales
1	USA	FOOD	12/30/2017	1254
2	USA	FOOD	09/30/2017	1154
3	USA	FOOD	06/30/2017	1200
4	USA	FOOD	03/30/2017	1500
1	USA	TOYS	12/30/2017	1478
2	USA	TOYS	09/30/2017	5684
3	USA	TOYS	06/30/2017	4859

On top of above query use case statement to create 4 quarter's columns

select e.country, e.category,  e.sales, e.date,
case when row_num= 1 then company_actual end as Q1,
case when row_num= 2 then company_actual end as Q2,
case when row_num= 3 then company_actual end as Q3,
case when row_num= 4 then company_actual end as Q4 from 

( 

select row_number() over (partition by country, category, sales, date_part('year', date) order by country, category asc, sales, date desc ) as row_num , * from tbl_sales 

) e order by 1,2

above query will generate below output:

row_num	country	category	date	sales	Q1	Q2	Q3	Q4
1	USA	FOOD	12/30/2017	1254	1254
2	USA	FOOD	09/30/2017	1154		1154
3	USA	FOOD	06/30/2017	1200			1200
4	USA	FOOD	03/30/2017	1500				1500
1	USA	TOYS	12/30/2017	1478	1478
2	USA	TOYS	09/30/2017	5684		5684
3	USA	TOYS	06/30/2017	4859			4859
4	USA	TOYS	03/30/2017	1548				1548

Now we just have to use group by query to get final result:

select country, category,
sum(Q1) Q1,
sum(Q2) Q2,
sum(Q3) Q3,
sum(Q4) Q4   from
(
select e.country, e.category,  e.sales,
case when row_num= 1 then company_actual end as Q1,
case when row_num= 2 then company_actual end as Q2,
case when row_num= 3 then company_actual end as Q3,
case when row_num= 4 then company_actual end as Q4 from
select row_number() over (partition by country, category, sales, date_part('year', date) order by country, category asc, sales, date desc ) as row_num,
* from tbl_sales  ) e
order by 1,2 ) B
group by 1,2 order by  1,2

Here we get transposed output:

country	category	Q1	Q2	Q3	Q4
USA	FOOD	1254	1154	1200	1500
USA	TOYS	1478	5684	4859	1548