clusteringKeyColumns

All clustering key columns of the primary table, stored alongside the partition key columns so a lookup resolution can reconstruct the primary table's full key (partition + clustering), not just its partition key. Empty for a primary table with no clustering key. See ISS-029: before this field existed, lookup resolution could only ever supply selectById with the partition key, which stopped being sufficient once ISS-025 made selectById require the full key on any clustering-keyed entity.