Know-How to Improve Query Performance in SQL Server

by Emily on May 6, 2020

in Articles

The primary function of the SQL database server is to store and retrieve the data which is requested by other software applications. SQL Server offers in different editions with respect to its features like Enterprise, Standard, Workgroup, Express. This database server is a computer program providing database service to other programs known as the client-server model. Hence, it is used for the execution of Structured Query Language.

It is quite often to suffer performance issues for SQL queries, as users want a fast response to the data retrieval process. This can be due to performance degradation of the improper maintenance of databases or queries are written inefficiently.

In order to maintain the database in proper form, there are various tips and tricks to improve query performance in SQL Server. This article focus on various techniques that one can follow to improve query performance in SQL Server.

Tips to Improve Query Performance in SQL Server

There are different workarounds available to improve query performance in SQL Server such as proper management of statistics, re-writing the SQL query, creation, and use of indexes, etc. Therefore, it is necessary to optimize queries to improve SQL performance.

  • Now start from Indexing the predicates in JOIN, WHERE, ORDER BY, and GROUP BY clauses.
    Without proper indexing, SQL queries can cause table scans which can decrease the performance. Hence, it is recommended that all predicate columns are indexed.
  • SQL server first searches the user-defined stored procedure from the master .mdf and then from the current database. Hence, avoid using a prefix with a user-defined stored procedure
  • Explore the tables used in the SELECT statement, so that filters can be applied in the WHERE clause. When there are queries with sub-selects, try to apply filters in the inner states of the sub-selects
  • Only the columns which are selected will be read while using a column-oriented DBMS aka Database Management System. Therefore, if less number of columns are included in the query, the lower I/O will occur.
  • After that, you need to remove the JOINS from the unnecessary tables which will help to lower the database processing time. Thus, by removing columns it is observed that data is recovered from the database.
  • In the SELECT statement, avoid writing *. For instance, provide the name of the column which is required.
  • If possible avoid using nchar and varchar, as both the data types take double memory as that of char and varchar.
  • Try to avoid NULL in a fixed-length field. If there is a requirement to use NULL, then use a varchar field which takes less space for NULL.
  • Avoid the HAVING clause, as this clause is required only if the user needs to filter the result of aggregations.
  • Now you need to generate clustered and non-clustered Indexes and keep clustered index small. Sometimes, it is also used in a non-clustered index.
  • It is a smart approach to create indexes columns that have integer values instead of characters. As character values takes more space than an integer value.
  • Use the WHERE clause to limit the size of the resultant tables which were created with joins.
  • Select the appropriate Data Type. For instance, if there is a need to store strings, then use varchar in place of the text data type. Try to use text data type, when there is a need to store large data which is more than 8000 characters.
  • You can increase query performance in SQL Server,  by using TABLOCKX while inserting into the table and by using TABLOCK while merging.
  • Try to use SET NOCOUNT ON and TRY- CATCH which will help to avoid the deadlock condition.
  • If the table variable is used in place of the temp table, it makes a great difference to improve SQL performance. As the use of temp tables requires interaction with the TempDb database which is a time-consuming task.
  • If UNION ALL is used in place of UNION, this increases the speed, and thus improves the SQL performance.
  • In case of frequently used and complex queries, use Stored Procedure for rapid data retrieval.
  • Multi-statement Table-Valued Functions (TVFs) are expensive in comparison to inline TVFs. Therefore, users should avoid using multi-statement TVFs.

Conclusion

Sometimes most of the SQL Server users face poor performance with SQL queries. By reading the various tips which are mentioned in this blog, one can practice it to improve query performance in SQL Server. This blog clearly explains the solutions to improve SQL performance by giving a few user queries also.

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