Index entries are stored as rows on index pages in a format similar to the format used for data rows on data pages. Index entries store the key values and pointers to lower levels of the index, to the data pages, or to individual data rows.
Adaptive Server uses B-tree indexing, so each node in the index structure can have multiple children.
Index entries are usually much smaller than a data row in a data page, and index pages are much more densely populated than data pages. If a data row has 200 bytes (including row overhead), there are 10 rows per page.
An index on a 15-byte field has about 100 rows per index page (the pointers require 4–9 bytes per row, depending on the type of index and the index level).
Indexes can have multiple levels: