Function returning varchar inside select - plsql

Question

Trying to generalize the SQL what splits a string/varchar into records. Here is the working SQL:
SELECT test.* FROM test JOIN (
SELECT level nbr, REGEXP_SUBSTR('1,3', '(.*?)(,|$)', 1, level, NULL, 1) value
FROM dual CONNECT BY level <= REGEXP_COUNT('1,3', ',')+1 ORDER BY level
) requested ON test.id=requested.value
What I mean by generalizing is; moving the recurring SQL (in this case the bit between the parenthesis's from the working SQL above) to a procedure/function so it can be reused. In this case I'm trying to find a way to insert a generated inner select statement. This is how the generalized SQL may look like:
SELECT t.* FROM table t JOIN (<GENERATED_INNER_SELECT>) my ON t.x=my.x;
However I didn't succeed yet, I tried tho but calling my function to generate the inner select statement directly resulted in:
ORA-00900: invalid SQL statement
And using the function in the generalized SQL resulted in:
ORA-00907: missing right parenthesis
None of these errors make any sense to me in this context.
Perhaps you can help? check out the full case on dbfiddle.

Answer 1

If you generate a SQL fragment to use as a subquery then the overall statement that embeds that as a subquery would have to be executed dynamically too.
It would be simpler to have the function actually doing the split itself, and returning a collection - as a schema-level collection type:
CREATE TYPE T_NUMBERS AS TABLE OF NUMBER
/
CREATE OR REPLACE FUNCTION split(p_string VARCHAR2, p_seperator VARCHAR2 DEFAULT ',')
RETURN T_NUMBERS AS
L_NUMBERS T_NUMBERS;
BEGIN
SELECT REGEXP_SUBSTR(p_string, '(.*?)(,|$)', 1, level, NULL, 1)
BULK COLLECT INTO L_NUMBERS
FROM dual
CONNECT BY level <= REGEXP_COUNT(p_string, ',')+1;
RETURN L_NUMBERS;
END split;
/
SELECT * FROM TEST
WHERE id MEMBER OF (split('1,3'))
/
ID NAM
---------- ---
1 foo
3 foe
or if you prefer the table collection expression approach:
SELECT t.*
FROM TABLE(split('1,3')) tmp
JOIN test t ON t.id = tmp.column_value;
It would be even simpler if the query could be called with a collection of numbers in the first place, but without seeing how the call is being made - and the string generated - it's hard to say exactly how you'd need to change that. You could even use a built-in collection type then, instead of having to define your own:
SELECT t.*
FROM TABLE(SYS.ODCINUMBERLIST(1,3)) tmp
JOIN test t ON t.id = tmp.column_value;
but it relies on the caller being able to pass the numbers in rather than a string (note the lack of single quotes...)