PostgreSQL: Count from x to y - postgresql

Question

How do I count in PostgreSQL from X to Y where X and Y come from table fields.
Similar to how a for loop works.
I tried to use ranges.

Answer 1

Use generate_series:
demo:db<>fiddle
It is not quiet clear what your data looks like:
A: You have one table with two columns x and y and exactly one row:
x | y
--+--
2 | 5
B: You have one table with two columns x and y and more than one row:
x | y
--+--
2 | 5
3 |10
It's not quiet clear what you mean with "count":
I.: You want one row per element:
count
-----
2
3
4
5
II.: You want an array of all elements:
count
-----
{2,3,4,5}
A.I: You have a table with two columns x and y with exactly one row and want one row per element:
SELECT generate_series(x, y)
FROM values;
Result as seen in I. above
B.I: You have many rows:
Same query, result is the union of the generated rows:
count
-----
2
3
4
5
3
4
5
6
7
8
9
10
A.II: One row, want an array:
You have to group your generated series
SELECT array_agg(gs)
FROM (
SELECT x, generate_series(x, y) as gs
FROM values
) s
GROUP BY x
Result as seen in II.
B.II: Many rows, want an array:
Same query, result looks like:
count
------------------
{2,3,4,5}
{3,4,5,6,7,8,9,10}