Using multilist column as foreign key reference - sql

Question

I have a table TABLEA that store data in a Columns which are basically multilist columns like this ColumnA ',2562,2563,2564,' and ColumnB with values ',121,122,123,'.
These column are actually foreign key values coming from another table.
Data is something like this in Table A.
ID NAME ColumnA ColumnB
1 ITEM1 ,2562,2563,2564, ,121,122,123
2 ITEM2 NULL ,6455,545,
3 ITEM3 ,1221,1546, NULL
4 ITEM4 NULL NULL
I want to join these columns with there parent tables and extract data.
I am hoping the result set would have 8 rows.
For example
ITEM ColumnA ColumB
ITEM1 2562 121
ITEM1 2563 122
ITEM1 2564 123
ITEM2 NULL 6455
ITEM2 NULL 545
....
I have tried this query with some help but this is not working when I try to use ColumnB as well and also it ignores the Items with NULL values.
The Column A is saving Ids of USER_GROUP table but ColumnB is fetching the Ids from some other table lets say GROUP1 and there could be another Column ColumnC that might be storing values from another table so that's kind of situation I am stuck in and hope I have explained so someone can understand but I am open if you want me to improve more
SELECT ug.*
FROM USER_GROUP ug
WHERE EXISTS (SELECT 1
FROM TableA t1
WHERE t1.COLUMNA LIKE '%,' || ug.ID || ',%'
)
AND EXISTS (SELECT 1
FROM TableA t1
WHERE t1.COLUMNB LIKE '%,' || ug.ID || ',%'
);

Answer 1

Here's one option:
SQL> with test (id, name, cola, colb) as
2 (select 1, 'item1', ',2562,2563,2564,', ',121,122,123,' from dual union all
3 select 2, 'item2', null , ',6455,545,' from dual union all
4 select 3, 'item3', ',1221,1546,' , null from dual union all
5 select 4, 'item4', null , null from dual
6 ),
7 remcom
8 -- remove leading and trailing commas
9 as (select id,
10 name,
11 rtrim(ltrim(cola, ','), ',') cola,
12 rtrim(ltrim(colb, ','), ',') colb
13 from test
14 )
15 select id,
16 name,
17 regexp_substr(cola, '[^,]+', 1, column_value) cola,
18 regexp_substr(colb, '[^,]+', 1, column_value) colb
19 from remcom r cross join
20 table(cast(multiset(select level from dual
21 connect by level <= regexp_count(nvl(r.cola, r.colb), ',') + 1
22 ) as sys.odcinumberlist))
23 order by id, name, cola, colb;
ID NAME COLA COLB
---------- ----- ---------- ----------
1 item1 2562 121
1 item1 2563 122
1 item1 2564 123
2 item2 545
2 item2 6455
3 item3 1221
3 item3 1546
4 item4
8 rows selected.
SQL>
Now that you have it, join this result with another table you have.
By the way, this example nicely shows what it is a bad idea to store multiple values into the same column. Don't do that.

Answer 2

You don't need to use (slow) regular expressions and can do it with simple string functions in a recursive sub-query factoring clause:
WITH split_data ( id, name, columna, columnb, starta, enda, startb, endb ) AS (
SELECT id,
name,
columna,
columnb,
INSTR(columna,',',1,1),
INSTR(columna,',',1,2),
INSTR(columnb,',',1,1),
INSTR(columnb,',',1,2)
FROM test_data
UNION ALL
SELECT id,
name,
columna,
columnb,
enda,
CASE WHEN enda = 0 THEN 0 ELSE INSTR(columna,',',enda+1,1) END,
endb,
CASE WHEN endb = 0 THEN 0 ELSE INSTR(columnb,',',endb+1,1) END
FROM split_data
WHERE enda > 0
OR endb > 0
)
SELECT id,
name,
CASE
WHEN starta = 0 THEN NULL
WHEN enda = 0 THEN SUBSTR( columna, starta + 1 )
ELSE SUBSTR( columna, starta + 1, enda - starta - 1 )
END AS valuea,
CASE
WHEN startb = 0 THEN NULL
WHEN endb = 0 THEN SUBSTR( columnb, startb + 1 )
ELSE SUBSTR( columnb, startb + 1, endb - startb - 1 )
END as valueb
FROM split_data
ORDER BY id, starta, startb;
Which for your test data:
CREATE TABLE test_data ( ID, NAME, ColumnA, ColumnB ) AS
SELECT 1, 'ITEM1', ',2562,2563,2564', ',121,122,123' FROM DUAL UNION ALL
SELECT 2, 'ITEM2', NULL, ',6455,545' FROM DUAL UNION ALL
SELECT 3, 'ITEM3', ',1221,1546', NULL FROM DUAL UNION ALL
SELECT 4, 'ITEM4', NULL, NULL FROM DUAL;
Outputs:
ID | NAME | VALUEA | VALUEB
-: | :---- | :----- | :-----
1 | ITEM1 | 2562 | 121
1 | ITEM1 | 2563 | 122
1 | ITEM1 | 2564 | 123
2 | ITEM2 | null | 6455
2 | ITEM2 | null | 545
3 | ITEM3 | 1221 | null
3 | ITEM3 | 1546 | null
4 | ITEM4 | null | null
db<>fiddle here