PL/SQL Replacing characters in a string using another table - sql

Question

I need to create function that replaces characters in a string to characters from another table. What I'm trying returns exactly the same string from the beginning. Table t_symbols is:
+-------------------+-------------------------+
| Symbol_to_replace | Symbol_in_return_string |
+-------------------+-------------------------+
| K | Ќ |
| k | ќ |
| X | Ћ |
| x | ћ |
| A | Є |
| a | є |
| H | Њ |
| h | њ |
| O | ¤ |
| o | µ |
| U | ¦ |
| u | ± |
| Y | ‡ |
| y | ‰ |
| I | І |
| i | і |
| G | Ѓ |
| g | ѓ |
+-------------------+-------------------------+
I need to use cursor and take characters from this table and not just nesting multiple REPLACE
create or replace function f_replace(text in varchar2) return varchar2 is
ResultText varchar2(2000);
begin
for cur in (select t.symbol_to_replace, t.symbol_in_return_string from
t_symbols t) loop
ResultText:= Replace(text, cur.symbol_to_replace,
cur.symbol_in_return_string);
end loop;
return(ResultText);
end f_replace;

Answer 1

SQL has a function exactly for this. It is not REPLACE (where indeed you would need multiple iterations); it's the TRANSLATE function.
If the table contents may change, and you need to write a function that looks things up in the table at the time it is called, you could do something like the function I show below.
I am showing a complete example: First I create a table that will store the required substitutions. I only include the first few substitutions, because I want to show how the behavior of the function changes as the table is being modified - without needing to change anything about the function. (Which is the whole point of this.)
Then I show the function definition, and I demonstrate how it works. Then I insert two more rows in the substitutions table and I run exactly the same query; the result will now reflect the longer "list" of substitutions, as needed.
create table character_substitutions ( symbol_to_replace, symbol_in_return_string )
as
select 'K', 'Ќ' from dual union all
select 'k', 'ќ' from dual union all
select 'X', 'Ћ' from dual union all
select 'x', 'ћ' from dual union all
select 'A', 'Є' from dual union all
select 'a', 'є' from dual
;
create or replace function my_character_substitutions ( input_str varchar2 )
return varchar2
deterministic
as
symbols_to_replace varchar2(4000);
symbols_to_return varchar2(4000);
begin
select listagg(symbol_to_replace ) within group (order by rownum),
listagg(symbol_in_return_string) within group (order by rownum)
into symbols_to_replace, symbols_to_return
from character_substitutions;
return translate(input_str, symbols_to_replace, symbols_to_return);
end;
/
select 'Kags' as input_str, my_character_substitutions('Kags') as replaced_str
from dual;
INPUT_STR REPLACED_STR
---------- ------------
Kags Ќєgs
OK, so now let's insert a couple more rows into the table and run the same query. Notice how now the g is also substituted for.
insert into character_substitutions ( symbol_to_replace, symbol_in_return_string )
select 'G', 'Ѓ' from dual union all
select 'g', 'ѓ' from dual
;
select 'Kags' as input_str, my_character_substitutions('Kags') as replaced_str
from dual;
INPUT_STR REPLACED_STR
---------- ------------
Kags Ќєѓs