How can I switch case for each letter in a string with SQL?

Question

I need to convert this into this using PostgreSQL

dxItw9a4 --> DXiTW9A4

Is there any function or way that is already set?

Answer 1

Here is a solution that works by splitting the string into a resultset of charaters using regexp_split_to_table(), then converts them to the opposite case and joins them again using aggregate function string_agg():

select 
    string_agg(case when c ~ '[a-z]' then upper(c) else lower(c) end, '') res
from (
    select * from regexp_split_to_table('dxItw9a4', '') as chars(c)
) x

Demo on DB Fiddle:

| res      |
| :------- |
| DXiTW9A4 |