Answer by Schwern for Functions to filter missing values in SQL and change them to null values

You can use nullif which returns null if both values match, otherwise it returns the first value.

select  some_int,  nullif(some_int, 0),  some_text,  nullif(some_text, '0')from some_table

nullif is specific to your problem. More generically you'd use a case.

select  some_int,  case some_int    when 0 then null    else some_int  end as "case",  some_text,  case some_text    when '0' then null    else some_text  end as "case"from some_table;

Demonstration.