使用交叉表的PostgreSQL查询

Question

Now, I am leaning postgreSQL. In the study, I found crosstab in postgreSQL. I tried to apply this function to my customized table, but it dose not work. please help!!

This is my Table

 year | type     | count 
------+----------+----
 2015 | AS       |  6
 2015 | HY       |  6
 2015 | KR       |  6
 2015 | SE       |  6
 2016 | AS       |  2
 2016 | HY       |  2
 2016 | KR       |  2
 2016 | SE       |  2
 2017 | AS       |  1
 2017 | HY       |  1
 2017 | KR       |  1
 2017 | SE       |  1
 2018 | AS       |  2
 2018 | HY       |  2
 2018 | KR       |  2
 2018 | SE       |  2

I want to change this table like this

year |  AS  |  HY  |  KR  |  SE  |
----------------------------------
2015 |   6  |   6  |   6  |   6  |
2016 |   2  |   2  |   2  |   2  |
2017 |   1  |   1  |   1  |   1  |
2018 |   2  |   2  |   2  |   2  |

To make that table, I designed query using crosstab, but dose not work!

Please Let me know the query of this problem.

Answer 1

You could achieve this without Crosstab , you can use Aggregate function.

Query :

select 
  year,
  max(counts) filter (where type = 'AS') as "AS",
  max(counts) filter (where type = 'HY') as "HY",
  max(counts) filter (where type = 'KR') as "KR",
  max(counts) filter (where type = 'SE') as "SE"
from
  tbl
group by
  year
order by 
  year asc 

Demo <> DB Fiddle

And if you are try learning Crosstab this answer are really great and explain really well about to do pivot use Crosstab .

• PostgreSQL Crosstab Query