Learn T-SQL Querying

Non-clustered indexes

While clustered indexes are typically chosen based on the structure of the data, non-clustered indexes are created to support the WHERE and JOIN clauses of our queries. Adding a non-clustered index on a column provides an efficient way to locate data based on values in that column. If we have simple queries with only one filter condition in the WHERE clause, a single-column non-clustered index may be sufficient, but if we have more complex queries, we may need more complex indexes. In some cases, SQL Server can use multiple single-column indexes to satisfy a WHERE clause that has more than one filter condition, but in many cases, it is more efficient to create multi-column, non-clustered indexes. The following rules ...