Indexálást

Indexálást, or indexing, is the process of creating a data structure that improves the speed of data retrieval operations on a database. Think of it like the index at the back of a book; instead of reading through the entire book to find a specific topic, you can quickly locate the relevant page number. In databases, an index is a separate data structure, often a B-tree or hash table, that stores a sorted copy of one or more columns from a table. This allows the database system to find rows matching specific query criteria much faster than it would if it had to scan the entire table.

When a query is executed, the database's query optimizer can choose to use an index if it determines that doing so will be more efficient. The index provides a direct path to the desired data, avoiding the need for a full table scan. This can significantly reduce query execution time, especially for large tables and queries that filter or sort data based on indexed columns. However, indexing is not without its costs. Creating and maintaining indexes requires disk space and can slow down data modification operations like inserts, updates, and deletes, as the index itself must also be updated. Therefore, choosing which columns to index and understanding the trade-offs between read performance and write performance is crucial for effective database management.