Metabase tries to change the table & column names to something more friendly. It’s not good in English and dreadful in anything else.
You can disable it in settings (I just set it to change _ to space).
Annoyingly, you’ll have to either rename your existing fields or delete then recreate the databases. If you’ve only just started, 2nd option is best.
Ok, it was not an issue with my database but with the renaming I did in SQL queries. Metabase was reworking the headers. I did what you suggested, “change _ to space” in settings and it worked.