Extract delimited data from a column into multiple rows with SQLite [duplicate] - sql

Question

I'm struggling to convert
a | a1,a2,a3
b | b1,b3
c | c2,c1
to:
a | a1
a | a2
a | a3
b | b1
b | b2
c | c2
c | c1
Here are data in sql format:
CREATE TABLE data(
"one" TEXT,
"many" TEXT
);
INSERT INTO "data" VALUES('a','a1,a2,a3');
INSERT INTO "data" VALUES('b','b1,b3');
INSERT INTO "data" VALUES('c','c2,c1');
The solution is probably recursive Common Table Expression.
Here's an example which does something similar to a single row:
WITH RECURSIVE list( element, remainder ) AS (
SELECT NULL AS element, '1,2,3,4,5' AS remainder
UNION ALL
SELECT
CASE
WHEN INSTR( remainder, ',' )>0 THEN
SUBSTR( remainder, 0, INSTR( remainder, ',' ) )
ELSE
remainder
END AS element,
CASE
WHEN INSTR( remainder, ',' )>0 THEN
SUBSTR( remainder, INSTR( remainder, ',' )+1 )
ELSE
NULL
END AS remainder
FROM list
WHERE remainder IS NOT NULL
)
SELECT * FROM list;
(originally from this blog post: https://blog.expensify.com/2015/09/25/the-simplest-sqlite-common-table-expression-tutorial)
It produces:
element | remainder
-------------------
NULL | 1,2,3,4,5
1 | 2,3,4,5
2 | 3,4,5
3 | 4,5
4 | 5
5 | NULL
the problem is thus to apply this to each row in a table.

Answer 1

Yes, a recursive common table expression is the solution:
with x(one, firstone, rest) as
(select one, substr(many, 1, instr(many, ',')-1) as firstone, substr(many, instr(many, ',')+1) as rest from data where many like "%,%"
UNION ALL
select one, substr(rest, 1, instr(rest, ',')-1) as firstone, substr(rest, instr(rest, ',')+1) as rest from x where rest like "%,%" LIMIT 200
)
select one, firstone from x UNION ALL select one, rest from x where rest not like "%,%"
ORDER by one;
Output:
a|a1
a|a2
a|a3
b|b1
b|b3
c|c2
c|c1

Answer 2

Check my answer in How to split comma-separated value in SQLite?.
This will give you the transformation in a single query rather than having to apply to each row.
-- using your data table assuming that b3 is suppose to be b2
WITH split(one, many, str) AS (
SELECT one, '', many||',' FROM data
UNION ALL SELECT one,
substr(str, 0, instr(str, ',')),
substr(str, instr(str, ',')+1)
FROM split WHERE str !=''
) SELECT one, many FROM split WHERE many!='' ORDER BY one;
a|a1
a|a2
a|a3
b|b1
b|b2
c|c2
c|c1