regexp_substr to bring back data before a foward slash - sql

Question

I have the following pattern of characters in a dataset. I need to manipulate the data & cross refer it to another table. I'm trying to write a regexp_substr to bring back data before a foward slash starting from the left. for example:-
abc/ab/123/zzz
so I need to get the following results back to then compare to another table
abc
abc/ab
abc/ab/123
I have worked out the other logic but an struggling with the various regexp.

Answer 1

Here is the recursive query with SUBSTR and INSTR:
with cte(col) as
(
select substr(col, 1, instr(col, '/', -1) - 1) from mytable
union all
select substr(col, 1, instr(col, '/', -1) - 1) from cte where instr(col, '/') > 0
)
select col from cte;
And here is the query with REGEXP_REPLACE:
with cte(col) as
(
select regexp_replace(col, '/[^/]*$', '') from mytable
union all
select regexp_replace(col, '/[^/]*$', '') from cte where instr(col, '/') > 0
)
select col from cte;

Answer 2

You don't need a regular expression. You can do it with (faster) string functions:
SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE test_data ( id, value ) AS
SELECT 1, 'abc/ab/123/zzz' FROM DUAL;
Query 1:
WITH bounds ( id, value, end_pos ) AS (
SELECT id,
value,
INSTR( value, '/', 1 )
FROM test_data
WHERE INSTR( value, '/', 1 ) > 0
UNION ALL
SELECT id,
value,
INSTR( value, '/', end_pos + 1 )
FROM bounds
WHERE INSTR( value, '/', end_pos + 1 ) > 0
)
SELECT id,
SUBSTR( value, 1, end_pos ) AS item
FROM bounds
ORDER BY id, end_pos
Results:
| ID | ITEM |
|----|-------------|
| 1 | abc/ |
| 1 | abc/ab/ |
| 1 | abc/ab/123/ |
However, if you did want to use regular expressions then you could do:
Query 2:
WITH bounds ( id, value, lvl, item ) AS (
SELECT id,
value,
1,
REGEXP_SUBSTR( value, '.*?/', 1, 1 )
FROM test_data
WHERE REGEXP_SUBSTR( value, '.*?/', 1, 1 ) IS NOT NULL
UNION ALL
SELECT id,
value,
lvl + 1,
item || REGEXP_SUBSTR( value, '.*?/', 1, lvl + 1 )
FROM bounds
WHERE REGEXP_SUBSTR( value, '.*?/', 1, lvl + 1 ) IS NOT NULL
)
SELECT id,
item
FROM bounds
Results:
| ID | ITEM |
|----|-------------|
| 1 | abc/ |
| 1 | abc/ab/ |
| 1 | abc/ab/123/ |