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A covering index in SQL Server is a nonclustered index that includes all the columns required by a query, allowing SQL Server to retrieve the data without accessing the base table. This can significantly improve query performance by reducing I/O operations.
Definition and Benefits
A covering index is a nonclustered index that contains all the data needed to satisfy a query. This means that the query can be executed entirely using the index, without needing to access the actual table data. This is beneficial because accessing data from an index is generally faster than accessing data from the table, especially if the index is in memory1.
Example
Consider a table Books with the following structure:
CREATE TABLE Books(BookID INT IDENTITY(10,5),Author VARCHAR(30),Title VARCHAR(50),Pages SMALLINT,PublicationYear SMALLINT)To create a covering index for a query that retrieves the Title and Pages columns, you can use the following SQL statement:
What are Covering Indexes and Covered Queries in …
a covering index is the one which gives every required column and in which SQL server don't have hop back to the clustered index to find any column. This is achieved using non-clustered index and using INCLUDE option to cover …
SQL Server Covering Indexes: Explained with Examples
2024年2月19日 · A covering index in SQL Server is basically a nonclustered index that references all the data that a particular query is asking for.
Covering Index in SQL Server with Key and Non-Key Columns
在mssqltips.com上查看更多信息Let’s start by answering the question, what’s a covering index? The simplest way to describe it is an index that includes every column for a specific query. Sometimes you hear this referred to as covering the query. For example, take the simple query below. If you want to cover the query, an index like the one below does the trick. …- 评论数: 1
- 发布日期: 2023年1月11日
Using Covering Indexes to Improve Query Performance
- Clustered index execution plan. The following Transact-SQL statement was …
- Nonclustered index execution plan. For more information on clustered …
- Key lookup operation properties. This Key Lookup operation was executed …
- Resorting to a table scan. The new query searches for a range of customers …
- Properties for the table scan operation. One may be tempted to force SQL …
Create indexes with included columns - SQL Server
2024年11月22日 · This article describes how to add included (or nonkey) columns to extend the functionality of nonclustered indexes in SQL Server by using SQL Server Management Studio …
SQL Server covering index and key lookup performance
2012年4月15日 · What is a covering index? A covering index is a non-clustered index which includes all columns referenced in the query and therefore, the optimizer does not have to perform an additional lookup to the table in order to …
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Increase Query Speed with Covering Indexes
2005年8月17日 · Improving the response times of queries in SQL Server is a common task for DBAs and developers. In this article, we will talk about how you can effectively use covered indexes to improve your...
Understanding the Covering Index in SQL - Database.Guide
2024年8月30日 · A covering index is an index that includes all the columns a query needs, whether it’s in the WHERE clause, SELECT list, JOIN clause, or ORDER BY clause. When a …
Mastering SQL Server Indexes: Unlock the Secrets of Clustered, …
2024年11月27日 · Indexes are critical to SQL Server performance. By understanding clustered, non-clustered, covering, and include indexes, you can fine-tune your queries for speed and …
Covering index: an index containing all queried columns - Use The Index …
To cover an entire query, an index must contain all columns from the SQL statement—in particular also the columns from the select clause as shown in the following example: …
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