Is it possible to perform multiple replacements in one function call? - sql

Question

If you want to replace multiple strings in one go, you can of course nest the REPLACE function, eg. like this:
SELECT REPLACE(REPLACE(REPLACE(foo, 'apple', 'fruit'), 'banana', 'fruit'), 'lettuce', 'vegetable')
FROM bar
If you have to do a lot of replacing, your code will become ugly and hard to read. Is there such a thing as a multi-replace function? Which would maybe take 2 arrays as arguments? To be sure, I'm familiar with the TRANSLATE function, but as my example indicates I want to replace whole words, not just single characters.

Answer 1

I would implement such a function in the following way:
CREATE OR REPLACE FUNCTION multi_replace(_string text, variadic _param_args text[])
RETURNS TEXT
AS
$BODY$
DECLARE
_index integer;
BEGIN
FOR _index IN 1 .. cardinality(_param_args) - 1 by 2 loop
_string := replace(_string, _param_args[_index], _param_args[_index+1]);
end loop;
RETURN _string;
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
cardinality() returns the length of the parameter array, and by 2 increases the loop index by 2 for every iteration so that it's safe to use _index and _index + 1 inside the loop to access the pairs that belong together.
Online example: https://rextester.com/LITG61720

Answer 2

I was looking for cleanliness, not performance, so I went with your suggestion 404.
This is the function I wrote:
CREATE OR REPLACE FUNCTION multi_replace(
_string TEXT,
VARIADIC _param_args TEXT[]
)
RETURNS TEXT AS
$BODY$
DECLARE
_old RECORD;
_new TEXT;
BEGIN
FOR _old in (
SELECT
_param_args[i] AS tekst,
i AS indexnummer
FROM generate_series(1, 5, 2) i
)
LOOP
_new := COALESCE(_param_args[_old.indexnummer+1], '');
_string := REPLACE(_string, _old.tekst, _new);
END LOOP;
RETURN _string;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
And this is a sample call:
select multi_replace('I love to drink milk in the morning', 'milk', 'beer', 'morning', 'evening', 'I', 'we');
Odd that this isn't a standard function, maybe a good idea for the next release? Thanks everybody for the suggestions!