Transpose single row with multiple columns into multiple rows of two columns - sql

Question

I have a SELECT query that works perfectly fine and it returns a single row with multiple named columns:
| registered | downloaded | subscribed | requested_invoice | paid |
|------------|------------|------------|-------------------|------|
| 9000 | 7000 | 5000 | 4000 | 3000 |
But I need to transpose this result to a new table that looks like this:
| type | value |
|-------------------|-------|
| registered | 9000 |
| downloaded | 7000 |
| subscribed | 5000 |
| requested_invoice | 4000 |
| paid | 3000 |
I have the additional module tablefunc enabled at PostgreSQL but I can't get the crosstab() function to work for this. What can I do?

Answer 1

You need the reverse operation of what crosstab() does. Some call it "unpivot". A LATERAL join to a VALUES expression should be the most elegant way:
SELECT l.*
FROM tbl -- or replace the table with your subquery
CROSS JOIN LATERAL (
VALUES
('registered' , registered)
, ('downloaded' , downloaded)
, ('subscribed' , subscribed)
, ('requested_invoice', requested_invoice)
, ('paid' , paid)
) l(type, value)
WHERE id = 1; -- or whatever
You may need to cast some or all columns to arrive at a common data type. Like:
...
VALUES
('registered' , registered::text)
, ('downloaded' , downloaded::text)
, ...
Related:
Postgres: convert single row to multiple rows (unpivot)
For the reverse operation - "pivot" or "cross-tabulation":
PostgreSQL Crosstab Query