When talking about SQL Server performance tuning and queries enhancement, the first thing to consider is the SQL Server Index. It serves to accelerate reading data from underlying tables by providing quick access to the requested rows. Thus, it won’t need to scan all the table’s records.

The SQL Server index provides those fast search capabilities due to the B-Tree structure of the index. This structure makes it possible to move through the table rows based on the index key quickly and retrieve the requested records at once. It won’t need to read the whole table.

SQL Server indexes’ types

Among the main types, we pay attention to the clustered and non-clustered indexes.

The **Clustered index **sorts the actual data in the data pages according to the clustered index key values. It stores the data at the “leaf” level of the index, ensuring the possibility to create only one clustered index on each table. The clustered index is created automatically when a Primary Key constraint appears on the heap table.

The **Non-clustered index **contains the index key value and a pointer to the rest of the row columns in the main table. It is the “leaf” level of the index, with the ability to create up to 999 non-clustered indexes on each table.

#SQL Server #indexes #query performance #sql server