A hash index must have a primary index. Unlike other base tables, you do not use the keywords PRIMARY INDEX to specify the primary index for a hash index.
The following table explains how the primary index for a hash index is defined:
| Hash Index | Primary Index for the Hash Index Uses this Column Set |
|---|---|
| Does not define a BY clause | Primary index of the base table to which the hash index refers. |
| Specifies a BY clause and an ORDER BY clause | Column set specified in the column_name_2 set in the BY clause. These columns must also be defined in the column_name_1 set. Rows in a hash index defined with this type of primary index are ordered either by row hash or by numeric value, depending on what you specify in the ORDER BY clause. |