The database system creates a B* tree for every index for which a base table is defined.
The index of a base table is defined explicitly with an SQL statement and has nothing to do with the B* tree index level.
The B* tree for the index of a base table is structured as follows:
· 1:1 relationship between the index entry and the value: value is stored directly in the leaf page of the B* tree of the index.
· 1:n relationship between the index entry and values: an additional sub-B* tree is created for the values, which is referenced by the leaf page of the B* tree of the index.
The following figure shows the B* trees for a base table that was defined for an index with multiple columns.