Everything Dev Needs to Know about SQL Server Update Statistics

Hello Dev, SQL Server is a popular relational database management system developed by Microsoft. It is used by many enterprises to store and manage their data. SQL Server provides various features to optimize database performance, and one of them is updating statistics. In this article, we will discuss everything you need to know about SQL Server update statistics.

What are Statistics in SQL Server?

Statistics are used by SQL Server to optimize query performance. They contain information about the distribution of data in a table or an index. SQL Server uses these statistics to determine the most efficient way to execute a query. When you execute a query, SQL Server analyzes the query and uses the statistics to create an execution plan.

There are two types of statistics in SQL Server:

What is SQL Server Update Statistics?

SQL Server update statistics is a feature that updates the statistics of a table or an index. SQL Server updates the statistics automatically when a table or an index is created or modified. However, in some cases, you may need to update the statistics manually to improve query performance.

When you update statistics, SQL Server uses the existing data in the table or the index to create new statistics. The new statistics can result in a different execution plan, which may improve query performance.

When to Update Statistics?

There are several scenarios where you should consider updating statistics manually:

1. Data Modifications

When you insert, update or delete a large amount of data in a table, the distribution of data in that table may change significantly. In this case, you should consider updating the statistics of that table.

2. Index Rebuild or Reorganize

When you rebuild or reorganize an index, the statistics of that index are also updated automatically. However, if you disable the automatic statistics update, you need to update the statistics manually after rebuilding or reorganizing the index.

3. Query Performance Issues

If you notice that the query performance has degraded significantly, you should check the statistics of the tables and indexes involved in that query. If the statistics are outdated, you should update them manually.

4. Too Many Rows Modified

If you modify more than 20% of the rows in a table, SQL Server will not update the statistics automatically. In this case, you should update the statistics manually.

5. Database Migration

When you migrate a database from one server to another, you need to update the statistics of all the tables and indexes in that database. This is because the distribution of data may be different in the new server, and the existing statistics may not be optimal.

How to Update Statistics in SQL Server?

You can update statistics in SQL Server using the following methods:

1. Using SQL Server Management Studio

You can update statistics of a table or an index using SQL Server Management Studio (SSMS). Right-click on the table or the index in the Object Explorer, and select “Properties”. In the “Properties” window, select “Statistics” from the left pane. You can then click on the “Update” button to update the statistics.

2. Using T-SQL

You can also update statistics using T-SQL. The syntax for updating statistics is as follows:

UPDATE STATISTICS table_or_index_name [ WITH [ FULLSCAN | SAMPLE number_rows ] ]

The “table_or_index_name” parameter specifies the name of the table or the index whose statistics you want to update. The “WITH” clause is optional and can be used to specify the type of scan to be used. The “FULLSCAN” option scans the entire table or index, while the “SAMPLE” option scans a specified number of rows.

FAQ

1. How often should you update statistics in SQL Server?

There is no one-size-fits-all answer to this question. You should update the statistics manually whenever you encounter one of the scenarios mentioned above.

2. Does updating statistics cause downtime?

No, updating statistics does not cause downtime. However, it may cause a temporary increase in CPU usage and disk I/O.

3. Can you update statistics in a transaction?

Yes, you can update statistics in a transaction.

4. Can you update statistics for a single column?

Yes, you can update statistics for a single column using the “CREATE STATISTICS” or “UPDATE STATISTICS” statement.

5. What is the difference between “FULLSCAN” and “SAMPLE”?

The “FULLSCAN” option scans the entire table or index, while the “SAMPLE” option scans a specified number of rows. The “FULLSCAN” option provides more accurate statistics, but it may take longer to complete.

That’s all for now, Dev. We hope this article has provided you with a good understanding of SQL Server update statistics. If you have any questions or comments, feel free to leave them below.