tableindex

A tableindex, in database terminology, refers to a data structure that accelerates the retrieval of rows from a table by providing quick access paths based on the values of one or more columns. It is separate from the data rows themselves and is maintained by the database system to reflect changes to the underlying table.

How it works: an index stores entries that map key values to pointers or references to the corresponding rows. Most common implementations use a balanced tree structure (such as a B-tree or B+ tree) to keep entries sorted, enabling efficient range and equality lookups. Other index types include hash indexes for fast equality lookups and bitmap or inverted indexes for specific workloads or text search. A well-designed index reduces the amount of data the system must scan, which speeds up queries that filter, join, or sort using the indexed columns. A covering index, which contains all columns needed by a query, can also satisfy the query without touching the table data.

Types and usage: primary or clustered indexes define the physical ordering of data in some database systems, while secondary (non-clustered) indexes exist separately and point to rows. Indexes can be single-column or composite (multi-column), and may enforce uniqueness. They are most beneficial on columns used in WHERE clauses, JOIN conditions, ORDER BY, or GROUP BY operations. However, every index adds maintenance overhead on inserts, updates, and deletes and consumes storage.

Design considerations: choose indexes with high selectivity, avoid over-indexing, and consider maintenance costs. In some systems, partial or filtered indexes cover specific query patterns, while full-text or inverted indexes suit large text search. Proper indexing can significantly improve read performance, but requires careful planning and monitoring to balance speed with write cost and storage.