Introduction to Indexing Strategies
Indexes are crucial for optimizing query performance in SQL Server. They provide a way to quickly locate rows in a table without scanning the entire table, significantly speeding up data retrieval. However, creating indexes also has a cost – they consume storage space and impact the time required to modify the table (inserts, updates, deletes).
Key Concepts
- Clustered Indexes: Determine the physical order of data in the table. Only one clustered index can exist per table.
- Non-Clustered Indexes: Store a copy of the indexed column(s) and a pointer to the row in the table. Multiple non-clustered indexes can exist per table.
- Covering Indexes: Include all the columns needed in a query, eliminating the need to access the base table.
- Filtered Indexes: Index only a subset of rows based on a specified filter condition.
When to Use Indexes
Consider creating indexes when:
- You frequently query columns used in `WHERE` clauses.
- You frequently join tables on columns that are not covered by a clustered index.
- You have a large table with many rows.