I wanted to change dataType of column from UUID to int4
ALTER TABLE tableA ALTER COLUMN columnA TYPE int4(32);
But it is giving me an error.
ERROR: type modifier is not allowed for type "int4"
I tried to search on internet and found that I have to use USING but don't know how to use it.
You cannot really turn a UID into an int. There are just too many values, so you run the risk of collisions (which rises to 100% as the table gets bigger).
My guess is that you really want an id column on the table. If so, add a new column and remove the old one:
alter table tableA add a_id int generated always as identity,
drop columnA;
Note: in older versions of Postgres, you would use serial instead of int generated always as identity.
Your 32 is syntactically treated as a modifier. Modifiers are allowed for numeric and decimal types, but not for plain ints, int4(xxx) is not a valid type in Postgres (I believe it is in mysql) int4 is just an alias for integer.
