The pg_partition_columns system view is used to show the partition key columns of a partitioned table.

column	type	references	description
schemaname	name		The name of the schema the partitioned table is in.
tablename	name		The table name of the top-level parent table.
columnname	name		The name of the partition key column.
partitionlevel	smallint		The level of this subpartition in the hierarchy.
position_in_partition_key	integer		For list partitions you can have a composite (multi-column) partition key. This shows the position of the column in a composite key.

Parent topic: System Catalogs Definitions