SQLindeksejä

SQLindeksejä, or SQL indexes, are database objects that improve the speed of data retrieval operations on a database table. They work by creating a data structure, such as a B-tree, that stores a sorted copy of one or more columns from a table. When a query is executed that needs to find data based on these indexed columns, the database can use the index to quickly locate the relevant rows instead of performing a full table scan.

Indexes are particularly beneficial for queries that involve WHERE clauses, JOIN operations, and ORDER BY clauses. By reducing the number of rows the database needs to examine, indexes can significantly speed up query execution, especially on large tables. However, indexes also have a cost. They consume disk space and can slow down data modification operations like INSERT, UPDATE, and DELETE because the index structure also needs to be updated. Therefore, it's important to create indexes strategically, only on columns that are frequently used in query conditions or joins, and to avoid over-indexing. Different types of indexes exist, such as clustered and non-clustered indexes, each with its own characteristics and use cases. The choice of index type and the columns to index depends on the specific database system and the typical workload.