Indexes in SQL server

Question

What is Index and types and when to use in real time

Jaish Mathews · Answer

What is an Index in SQL Server? An index in SQL Server is a database object that improves the speed of data retrieval operations on a table at the cost of additional storage and maintenance during data modification operations (e.g. INSERT  UPDATE  DELETE ). It acts like a lookup table that helps the database find rows quickly. Types of Indexes in SQL Server 1. Clustered Index Description : Sorts and stores the data rows in the table based on the key values of the index. A table can have only one clustered index. Storage : Data rows are stored in the same order as the index. When to Use : When the data is queried in a specific order frequently (e.g. range queries like dates). On columns that are unique and often used for sorting or filtering. Example : CREATE CLUSTERED INDEX idx_EmployeeID ON Employees(EmployeeID); 2. Non-Clustered Index Description : Contains pointers to the actual data in the table not the data itself. A table can have multiple non-clustered indexes. Storage : Stores index structure separately from the actual data. When to Use : On columns used in WHERE  JOIN  or GROUP BY clauses that are not part of the clustered index. For frequently queried columns that do not define the data's physical order. Example : CREATE NONCLUSTERED INDEX idx_LastName ON Employees(LastName); 3. Unique Index Description : Ensures that all values in the indexed column(s) are unique. Can be clustered or non-clustered. When to Use : On columns that require uniqueness such as email addresses or usernames. Example : CREATE UNIQUE INDEX idx_Unique_Email ON Users(Email); 4. Composite Index Description : An index on two or more columns. When to Use : When queries frequently filter or sort by multiple columns together. Example : CREATE NONCLUSTERED INDEX idx_Composite ON Orders(CustomerID OrderDate); 5. Filtered Index Description : A non-clustered index with a filter condition to index a subset of rows. When to Use : On columns with sparse data (e.g. where many rows have NULLs or specific values are queried often). Example : CREATE NONCLUSTERED INDEX idx_Filtered ON Sales(Total) WHERE Total > 1000; 6. Full-Text Index Description : Supports full-text search on large text data such as finding words or phrases in a text column. When to Use : On large text columns when performing searches for words phrases or patterns. Example : CREATE FULLTEXT INDEX ON Articles(Content) KEY INDEX PK_ArticleID; 7. XML Index Description : Used to index XML data stored in an XML data type column. When to Use : When querying XML data frequently. Example : CREATE PRIMARY XML INDEX idx_XML_Data ON Orders(XMLData); 8. Columnstore Index Description : Stores data in a columnar format rather than rows optimizing for analytical and reporting workloads. When to Use : For large datasets and analytical queries in data warehousing. Example : CREATE CLUSTERED COLUMNSTORE INDEX idx_ColumnStore ON SalesData; 9. Spatial Index Description : Indexes spatial data types (e.g. geography geometry). When to Use : When working with geospatial data (e.g. GIS applications). Example : CREATE SPATIAL INDEX idx_Spatial ON Locations(GeoData); When to Use Indexes in Real-Time Frequent Searches : Use indexes on columns that are frequently used in WHERE  JOIN  or GROUP BY clauses to speed up searches. Sorting and Ordering : Apply indexes to columns often used in ORDER BY clauses to avoid sorting overhead. Unique Constraints : Use a unique index to enforce data integrity for columns that must have unique values such as email addresses or employee IDs. Range Queries : Clustered indexes work well for range queries (e.g. date ranges). Sparse Data : Use filtered indexes for columns with many NULL values or specific ranges of values. Analytical Workloads : Use columnstore indexes for reporting and analytical queries. Text Searches : Apply full-text indexes to text columns for advanced search capabilities. Considerations and Best Practices Avoid Over-Indexing : Too many indexes can slow down INSERT  UPDATE  and DELETE operations. Monitor Usage : Use SQL Server’s sys.dm_db_index_usage_stats to track index usage and identify unused indexes. Rebuild and Reorganize : Regularly rebuild or reorganize fragmented indexes to maintain performance. Covering Index : Use included columns in non-clustered indexes to create covering indexes that reduce lookups. Indexes when used strategically significantly enhance query performance but require careful planning and maintenance to avoid performance degradation.

Tuhin Paul · Answer

Indexes are used to improve the performance of queries by allowing the database engine to find and retrieve data more efficiently. Here are the main types of indexes available in SQL Server. Hope this helps.

Rajanikant Hawaldar · Answer

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