MySQL 5.7

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create table myTable (phone varchar(100));
insert into myTable values ('1234567890');
insert into myTable values ('1234567890');
insert into myTable values ('00382234567890');
insert into myTable values ('+382234567890');
insert into myTable values ('382234567890');
select distinct case when length(phone) = 10 then concat('00382', right(phone ,(length(phone)-1)))
                     when length(phone) = 13 then replace(phone, '+', '00')
                     when length(phone) = 12 then concat ('00', phone)
                     else phone
                end 
from myTable;                     


case when length(phone) = 10 then concat('00382', right(phone ,(length(phone)-1)))
                     when length(phone) = 13 then replace(phone, '+', '00')
                     when length(phone) = 12 then concat ('00', phone)
                     else


00382234567890