How to get the current_row in a main query for a subquery? - sqlite

Question

Let assume the following table:
CREATE TABLE t1 (col1 TEXT PRIMARY KEY, value INTEGER);
INSERT INTO t1 VALUES
('IE/a', 1), ('IE/b', 2), ('IE/c', 3) ,
('00/a', 10), ('01/a', 20), ('02/a', 30), ('03/a', 40),
('00/b', 100), ('01/b', 200), ('02/b', 300), ('03/b', 400),
('00/c', 1000), ('01/c', 2000), ('02/c', 3000), ('03/c', 4000);
The content of the table is:
col1 value
IE/a 1
IE/b 2
IE/c 3
00/a 10
01/a 20
02/a 30
03/a 40
00/b 100
01/b 200
02/b 300
03/b 400
00/c 1000
01/c 2000
02/c 3000
03/c 4000
I want to get the following output:
IE/a 100
IE/b 1000
IE/c 10000
So, IE/a is the sum of the values of 00/a + 01/a + 02/a + 03/a.
My first approach looks like this, where current_row_id as my pseudeo_code_variable to demonstrate that a would like to consider the current row:
SELECT
col1
, (SELECT sum(value) FROM t1
WHERE col1 = '00' || SUBSTRING( current_row_col1, 3)
OR col1 = '01' || SUBSTRING( current_row_col1, 3)
OR col1 = '02' || SUBSTRING( current_row_col1, 3)
OR col1 = '03' || SUBSTRING( current_row_col1, 3)
) AS value
FROM t1
WHERE col1 LIKE 'IE/%';

Answer 1

Use a self join and aggregation:
SELECT t1.col1,
TOTAL(t2.value) AS total
FROM tablename t1 LEFT JOIN tablename t2
ON SUBSTR(t2.col1, INSTR(t2.col1, '/') + 1) = SUBSTR(t1.col1, INSTR(t1.col1, '/') + 1)
AND t2.rowid <> t1.rowid
WHERE t1.col1 LIKE 'IE/%'
GROUP BY t1.col1;
Or, with conditional aggregation:
SELECT MAX(CASE WHEN col1 LIKE 'IE/%' THEN col1 END) AS col1,
TOTAL(CASE WHEN col1 NOT LIKE 'IE/%' THEN value END) AS total
FROM tablename
GROUP BY SUBSTR(col1, INSTR(col1, '/') + 1);
Or, with window functions:
SELECT DISTINCT
MAX(CASE WHEN col1 LIKE 'IE/%' THEN col1 END) OVER (PARTITION BY SUBSTR(col1, INSTR(col1, '/') + 1)) AS col1,
TOTAL(CASE WHEN col1 NOT LIKE 'IE/%' THEN value END) OVER (PARTITION BY SUBSTR(col1, INSTR(col1, '/') + 1)) AS total
FROM tablename;
See the demo.

Answer 2

This should give you your expected results.
Remember when working with additional categories like ['IE/g'] you will need to add last letters to the conditional statement in where clause.
I used val instead of value as a column name because in many DBMS it's a restricted keyword.
Code:
select 'IE/' || substr(col1,4,1) col, sum(val) my_sum from t1 where col1 LIKE '%/%' and col1 not like 'IE/%' and substr(col1,4,1) in ('a', 'b', 'c') group by substr(col1,4,1);
Output:
col my_sum
IE/a 100
IE/b 1000
IE/c 10000