Replace all ', , ' inside string

Question

i have long string and with pl/sql i want to replace all ', ,' with ', null,'.
I can use replace function like:
prepare_insert := replace(prepare_insert,', ,',', null,');
but it will only replace first ', ,' not all. How can i replace all?

Answer 1

5th database commandment:
Thou shalt not create dynamic insert statements!
I think using bind variables or the using clause in the execute immediate statement would solve the problem.
But of cause you can do it also the hard (and slow) way.
The problem is that your search string is not correct. It does include a leading "," and leaving ",". However if the leavaing "," is also the leading "," of the next replacement part then the function can't take this into account.
Solution 1) Take care of this while building the string in the first place.
While concating the pieces togeather use NVL(value,'null'). If you are sure that there s no value, then write NULL.
Solution 2) Use a double replace
with testdata as (select 'Test, , , , ''ABC''' txt from dual union all
                  select 'Test2, , , ''ABC''' txt from dual
select txt
      ,replace(replace(txt,', ,',',null,'),', ,',',null,')
from testdata;
TXT               REPLACE
Test, , , , 'ABC'     Test,null,null,null, 'ABC'
Test2, , , 'ABC'     Test2,null,null, 'ABC'