Get even / odd / all numbers between two numbers - sql

Question

I want to display all the numbers (even / odd / mixed) between two numbers (1-9; 2-10; 11-20) in one (or two) column.
Example initial data:
| rang | | r1 | r2 |
-------- -----|-----
| 1-9 | | 1 | 9 |
| 2-10 | | 2 | 10 |
| 11-20 | or | 11 | 20 |
CREATE TABLE initialtableone(rang TEXT);
INSERT INTO initialtableone(rang) VALUES
('1-9'),
('2-10'),
('11-20');
CREATE TABLE initialtabletwo(r1 NUMERIC, r2 NUMERIC);
INSERT INTO initialtabletwo(r1, r2) VALUES
('1', '9'),
('2', '10'),
('11', '20');
Result:
| output |
----------------------------------
| 1,3,5,7,9 |
| 2,4,6,8,10 |
| 11,12,13,14,15,16,17,18,19,20 |

Answer 1

Something like this:
create table ranges (range varchar);
insert into ranges
values
('1-9'),
('2-10'),
('11-20');
with bounds as (
select row_number() over (order by range) as rn,
range,
(regexp_split_to_array(range,'-'))[1]::int as start_value,
(regexp_split_to_array(range,'-'))[2]::int as end_value
from ranges
)
select rn, range, string_agg(i::text, ',' order by i.ordinality)
from bounds b
cross join lateral generate_series(b.start_value, b.end_value) with ordinality i
group by rn, range
This outputs:
rn | range | string_agg
---+-------+------------------------------
3 | 2-10 | 2,3,4,5,6,7,8,9,10
1 | 1-9 | 1,2,3,4,5,6,7,8,9
2 | 11-20 | 11,12,13,14,15,16,17,18,19,20

Answer 2

Building on your first example, simplified, but with PK:
CREATE TABLE tbl1 (
tbl1_id serial PRIMARY KEY -- optional
, rang text -- can be NULL ?
);
Use split_part() to extract lower and upper bound. (regexp_split_to_array() would be needlessly expensive and error-prone). And generate_series() to generate the numbers.
Use a LATERAL join and aggregate the set immediately to simplify aggregation. An ARRAY constructor is fastest in this case:
SELECT t.tbl1_id, a.output -- array; added id is optional
FROM (
SELECT tbl1_id
, split_part(rang, '-', 1)::int AS a
, split_part(rang, '-', 2)::int AS z
FROM tbl1
) t
, LATERAL (
SELECT ARRAY( -- preserves rows with NULL
SELECT g FROM generate_series(a, z, CASE WHEN (z-a)%2 = 0 THEN 2 ELSE 1 END) g
) AS output
) a;
AIUI, you want every number in the range only if upper and lower bound are a mix of even and odd numbers. Else, only return every 2nd number, resulting in even / odd numbers for those cases. This expression implements the calculation of the interval:
CASE WHEN (z-a)%2 = 0 THEN 2 ELSE 1 END
Result as desired:
output
-----------------------------
1,3,5,7,9
2,4,6,8,10
11,12,13,14,15,16,17,18,19,20
You do not need WITH ORDINALITY in this case, because the order of elements is guaranteed.
The aggregate function array_agg() makes the query slightly shorter (but slower) - or use string_agg() to produce a string directly, depending on your desired output format:
SELECT a.output -- string
FROM (
SELECT split_part(rang, '-', 1)::int AS a
, split_part(rang, '-', 2)::int AS z
FROM tbl1
) t
, LATERAL (
SELECT string_agg(g::text, ',') AS output
FROM generate_series(a, z, CASE WHEN (z-a)%2 = 0 THEN 2 ELSE 1 END) g
) a;
Note a subtle difference when using an aggregate function or ARRAY constructor in the LATERAL subquery: Normally, rows with rang IS NULLare excluded from the result because the LATERAL subquery returns no row.
If you aggregate the result immediately, "no row" is transformed to one row with a NULL value, so the original row is preserved. I added demos to the fiddle.
SQL Fiddle.
You do not need a CTE for this, which would be more expensive.
Aside: The type conversion to integer removes leading / training white space automatically, so a string like this works as well for rank: ' 1 - 3'.