I don't want to know all data types, just all data types used in my database. Can this information be queried?
PostgreSQL 8.4 and 9.x versions
I currently need to know all data types for over 200 tables in public ( and other schemas )
select data_type, count(*) from information_schema.columns where table_schema = 'public' group by data_type ;
For other schemas just add: or table_schema = 'your_schema_name'.
If this will not satisfy you, you should look in pg_... or information_schema tables.
If you are looking for table information:
select data_type, count(*) from information_schema.columns where table_schema = 'public' and table_name = 'your_table_name' group by data_type ;