Conditional regexp_replace Oracle / PLSQL - sql

Question

I'm trying to do a conditional replace within one regexp_replace statement.
For example, if I have the string, 'Dog Cat Donkey', I would like to be able to replace 'Dog' with 'BigDog', 'Cat' with 'SmallCat' and 'Donkey' with 'MediumDonkey' to get the following:
'BigDog SmallCat MediumDonkey'
I can do it where all are prefixed with the word Big but can't seem to make it replace conditionally.
I currently have this
select regexp_replace('Dog Cat Donkey', '(Cat)|(Dog)|(Donkey)', ' Big\1\2\3')
from dual
but of course this only returns 'BigDog BigCat BigDonkey'.
I'm aware this isn't the best way of doing this but is it possible?

Answer 1

Have you considered just doing multiple replace()s?
select replace(replace(replace(str, 'Dog', 'BigDog'), 'Cat', 'SmallCat'), 'Donkey', 'MediumDonkey')
I get that regexp_replace() is really powerful. And it might be able to do this. But I'm not sure that's a better solution in terms of expressing what you are doing.

Answer 2

Query -
select listagg(final_str,' ') within group (order by sort_str) as output from (
SELECT
CASE LST
WHEN 'Dog' THEN 'BigDog'
WHEN 'Cat' THEN 'SmallCat'
WHEN 'Donkey' THEN 'MediumDonkey'
END AS final_str,
CASE LST
WHEN 'Dog' THEN 1
WHEN 'Cat' THEN 2
WHEN 'Donkey' THEN 3
END AS sort_str
from (
SELECT
trim(REGEXP_SUBSTR('Dog Cat Donkey', '(\S*)(\s*)', 1, LEVEL)) AS LST
FROM
DUAL
CONNECT BY
REGEXP_SUBSTR('Dog Cat Donkey', '(\S*)(\s*)', 1, LEVEL) IS NOT NULL
));
Output -
BigDog SmallCat MediumDonkey

Answer 3

For conditional replacement via REGEX_REPLACE?
Then currently you can do this by repeating it for each different replacement string.
But you could still use the | (OR) within the 1 capture group to change more than 1 word for the same replacement string.
And as Gordon Linoff pointed out.
You don't really need a REGEX_REPLACE when a normal REPLACE is sufficient to match a single word.
select regexp_replace(
regexp_replace(
regexp_replace( str,
'(Dog|Snoopy)', 'Big\1')
,'(Cat|Feline)', 'Small\1')
,'(Donkey|Ass)', 'Medium\1')
from (select 'You Ass, that is not a Dog, but a Cat on a Donkey.' as str from dual);
Returns:
You MediumAss, that is not a BigDog, but a SmallCat on a MediumDonkey.
Do note however that when using the pipe in a regex, that the order matters.
So if some words start the same then better put them in order of descending length.
Example:
select
regexp_replace(str, '(foo|foobar)', '[\1]') as foo_foobar,
regexp_replace(str, '(foobar|foo)', '[\1]') as foobar_foo
from (select 'foo foobar' as str from dual);
Returns:
FOO_FOOBAR FOOBAR_FOO
--------------- ---------------
[foo] [foo]bar [foo] [foobar]