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

Table 1. pg_catalog.pg_partition_columns

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.