Regex: How to Implement Negative Lookbehind in PL/SQL - regex

Question

How do I match all the strings that begin with loockup. and end with _id but not prefixed by msg? Here below are some examples:
lookup.asset_id -> should match
lookup.msg_id -> shouldn't match
lookup.whateverelse_id -> should match
I know Oracle does not support negative lookbehind (i.e. (?<!))... so I've tried to explicitly enumerate the possibilities using alternation:
regexp_count('i_asset := lookup.asset_id;', 'lookup\.[^\(]+([^m]|m[^s]|ms[^g])_id') <> 0 then
dbms_output.put_line('match'); -- this matches as expected
end if;
regexp_count('i_msg := lookup.msg_id;', 'lookup\.[^\(]+([^m]|m[^s]|ms[^g])_id') <> 0 then
dbms_output.put_line('match'); -- this shouldn’t match
-- but it does like the previous example... why?
end if;
The second regexp_count expression should't match... but it does like the first one. Am I missing something?
EDIT
In the real use case, I've a string that contains PL/SQL code that might contains more than one lookup.xxx_id instances:
declare
l_source_code varchar2(2048) := '
...
curry := lookup.curry_id(key_val => ''CHF'', key_type => ''asset_iso'');
asset : = lookup.asset_id(key_val => ''UBSN''); -- this is wrong since it does
-- not specify key_type
...
msg := lookup.msg_id(key_val => ''hello''); -- this is fine since msg_id does
-- not require key_type
';
...
end;
I need to determine whether there is at least one wrong lookup, i.e. all occurrences, except lookup.msg_id, must also specify the key_type parameter.

Answer 1

With lookup\.[^\(]+([^m]|m[^s]|ms[^g])_id, you are basically asking to check for a string
starting with lookup. denoted by lookup\.,
followed by at least one character different from ( denoted by [^\(]+,
followed by either -- ( | | )
one character different from m -- [^m], or
two characters: m plus no s -- m[^s], or
three characters: ms and no g -- ms[^g], and
ending in _id denoted by _id.
So, for lookup.msg_id, the first part matches obviously, the second consumes ms, and leaves the g for the first alternative of the third.
This could be fixed by patching up the third part to be always three characters long like lookup\.[^\(]+([^m]..|m[^s.]|ms[^g])_id. This, however, would fail everything, where the part between lookup. and _id is not at least four characters long:
WITH
Input (s, r) AS (
SELECT 'lookup.asset_id', 'should match' FROM DUAL UNION ALL
SELECT 'lookup.msg_id', 'shouldn''t match' FROM DUAL UNION ALL
SELECT 'lookup.whateverelse_id', 'should match' FROM DUAL UNION ALL
SELECT 'lookup.a_id', 'should match' FROM DUAL UNION ALL
SELECT 'lookup.ab_id', 'should match' FROM DUAL UNION ALL
SELECT 'lookup.abc_id', 'should match' FROM DUAL
)
SELECT
r, s, INSTR(s, 'lookup.msg_id') has_msg, REGEXP_COUNT(s , 'lookup\.[^\(]+([^m]..|m[^s]|ms[^g])_id') matched FROM Input
;
| R | S | HAS_MSG | MATCHED |
|-----------------|------------------------|---------|---------|
| should match | lookup.asset_id | 0 | 1 |
| shouldn't match | lookup.msg_id | 1 | 0 |
| should match | lookup.whateverelse_id | 0 | 1 |
| should match | lookup.a_id | 0 | 0 |
| should match | lookup.ab_id | 0 | 0 |
| should match | lookup.abc_id | 0 | 0 |
If you have just to make sure, there is no msg in the position in question, you might want to go for
(INSTR(s, 'lookup.msg_id') = 0) AND REGEXP_COUNT(s, 'lookup\.[^\(]+_id') <> 0
For code clarity REGEXP_INSTR(s, 'lookup\.[^\(]+_id') > 0 might be preferable…
#j3d Just comment if further detail is required.

Answer 2

With the requirements still being kind of vague…
Split the string at the semicolon.
Check each substring s to comply:
WITH Input (s) AS (
SELECT ' curry := lookup.curry_id(key_val => ''CHF'', key_type => ''asset_iso'');' FROM DUAL UNION ALL
SELECT 'curry := lookup.curry_id(key_val => ''CHF'', key_type => ''asset_iso'');' FROM DUAL UNION ALL
SELECT 'asset := lookup.asset_id(key_val => ''UBSN'');' FROM DUAL UNION ALL
SELECT 'msg := lookup.msg_id(key_val => ''hello'');' FROM DUAL
)
SELECT
s
FROM Input
WHERE REGEXP_LIKE(s, '^\s*[a-z]+\s+:=\s+lookup\.msg_id\(key_val => ''[a-zA-Z0-9]+''\);$')
OR
((REGEXP_INSTR(s, '^\s*[a-z]+\s+:=\s+lookup\.msg_id') = 0)
AND (REGEXP_INSTR(s, '[(,]\s*key_type') > 0)
AND (REGEXP_INSTR(s,
'^\s*[a-z]+\s+:=\s+lookup\.[a-z]+_id\(( ?key_[a-z]+ => ''[a-zA-Z_]+?'',?)+\);$') > 0))
;
| S |
|--------------------------------------------------------------------------|
|[tab] curry := lookup.curry_id(key_val => 'CHF', key_type => 'asset_iso');|
| curry := lookup.curry_id(key_val => 'CHF', key_type => 'asset_iso');|
| msg := lookup.msg_id(key_val => 'hello');|
This would tolerate a superfluous comma right before the closing parenthesis. But if the input is syntactically correct, such a comma won't exist.