SELECT
pg_attribute.attname,
format_type(pg_attribute.atttypid, pg_attribute.atttypmod)
FROM pg_index, pg_class, pg_attribute, pg_namespace
WHERE
pg_class.oid = 'my_table_name'::regclass AND
indrelid = pg_class.oid AND
nspname = 'my_schema_name' AND
pg_class.relnamespace = pg_namespace.oid AND
pg_attribute.attrelid = pg_class.oid AND
pg_attribute.attnum = any(pg_index.indkey)
AND indisprimary
See official version: http://wiki.postgresql.org/wiki/Retrieve_primary_key_columns
See also:
How to get primary key of a table from SQLite
How to get primary key of a table from MySQL
How to get primary key of a table from SQL Server
How to get primary key of a table from DB2
How to get primary key of a table from Oracle
Some PostgreSQL tools you can try: https://www.withdata.com/postgresql/
