SQL indexes are a way to improve the performance of a database by helping it find the data that it needs. They can be classified into different types based on their usage and their impact on the database. The most common types of SQL indexes are B-Tree indices, covering indexes, and hash indexes.
A B-Tree index is a data structure that organizes the data using a tree. The tree has a root node and branches that contain nodes. The index can be sorted or unsorted. The root node contains all of the records in the table while each branch contains pointers to other branches in order to find other records.
Clustered indexes are more efficient than non-clustered indexes because they can access the data in the index without scanning all of the data.
A primary index is an index that is created by a database administrator, usually when the database is first created. A secondary index is an index that has been created after the primary index.
Indexes are a way to organize data in order to make it more easily searchable. They can be used in SQL queries, but they are not the only way to search through data.
