SQLite: Use subquery result in another subquery - sql

Question

I have following table with data
id | COL1
=========
1 | b
2 | z
3 | b
4 | c
5 | b
6 | a
7 | b
8 | c
9 | a
So i know ID of 'z' (ID = 2) in the table and i will call it Z_ID.
I need to retrieve rows between 'a' and 'c' (including 'a' and 'c').
It must be first 'a' that comes after Z_ID.
'c' must come after Z_ID and after 'a' that i found previously.
Result that i am seeking is:
id | COL1
=========
6 | a
7 | b
8 | c
My SELECT looks like this
SELECT *
FROM table
WHERE id >= (
SELECT MIN(ID)
FROM table
WHERE COL1 = 'a' AND ID > 2
)
AND id <= (
SELECT MIN(ID)
FROM table
WHERE COL1 = 'c'AND ID > 2 and ID > (
SELECT MIN(ID)
FROM table
WHERE COL1 = 'a' AND ID > 2
)
)
I am getting the result that i want. But i am concerned about performance because i am using same subquery two times. Is there a way to reuse a result from first subquery?
Maybe there is cleaner way to get the result that i need?

Answer 1

Use a CTE which will return only once the result of the subquery that you use twice:
WITH cte AS (
SELECT MIN(ID) minid
FROM tablename
WHERE COL1 = 'a' AND ID > 2
)
SELECT t.*
FROM tablename t CROSS JOIN cte c
WHERE t.id >= c.minid
AND t.id <= (
SELECT MIN(ID)
FROM tablename
WHERE COL1 = 'c' and ID > c.minid
)
In your 2nd query's WHERE clause:
WHERE COL1 = 'c'AND ID > 2 and ID > (...
the condition AND ID > 2 is not needed because the next condition and ID > (... makes sure that ID will be greater than 2 so I don't use it either in my code.
See the demo.
Results:
| id | COL1 |
| --- | ---- |
| 6 | a |
| 7 | b |
| 8 | c |

Answer 2

You can use window functions for this:
select t.*
from (select t.*,
min(case when id > min_a_id and col1 = 'c' then id end) over () as min_c_id
from (select t.*,
min(case when col1 = 'a' then id end) over () as min_a_id
from (select t.*,
min(case when col1 = 'z' then id end) over () as z_id
from t
) t
where id > z_id
) t
) t
where id >= min_a_id and id < min_c_id;