Specifying Partitioning on Key Columns

For range-partitioned and hash partitioned tables, you can specify up to 16 partitioning key columns. Use multicolumn partitioning when the partitioning key is composed of several columns and subsequent columns define a higher granularity than the preceding ones. The most common scenario is a decomposed DATE or TIMESTAMP key, consisting of separated columns, for year, month, and day.

In evaluating multicolumn partitioning keys, the database uses the second value only if the first value cannot uniquely identify a single target partition, and uses the third value only if the first and second do not determine the correct partition, and so forth. A value cannot determine the correct partition only when a partition bound exactly matches that value and the same bound is defined for the next partition. The nth column is investigated only when all previous (n-1) values of the multicolumn key exactly match the (n-1) bounds of a partition. A second column, for example, is evaluated only if the first column exactly matches the partition boundary value. If all column values exactly match all of the bound values for a partition, then the database determines that the row does not fit in this partition and considers the next partition for a match.

For nondeterministic boundary definitions (successive partitions with identical values for at least one column), the partition boundary value becomes an inclusive value, representing a "less than or equal to" boundary. This is in contrast to deterministic boundaries, where the values are always regarded as "less than" boundaries.

This sections contains the following topics: