How Indexes Can Help You Write Better SQL Queries

by Aug 20, 2021

Categories

Tags

Administration agent-based monitoring Agentless Monitoring alert responses alert thresholds alerting Alerts Amazon Aurora Amazon EC2 Amazon RDS Amazon RDS / Aurora Amazon RDS for SQL Server Amazon Redshift Amazon S3 Amazon Web Services (AWS) Analytics application monitoring Aqua Data Studio automation availability Azure Azure SQL Database azure sql managed instance Azure VM backup Backup and recovery backup and restore backup compression backup status Backup Strategy backups big data Blocking bug fixes business architecture business data objects business intelligence business process modeling business process models capacity planning change management cloud cloud database cloud database monitoring cloud infrastructure cloud migration cloud providers Cloud Readiness Cloud Services cloud storage cloud virtual machine cloud VM clusters code completion collaboration compliance compliance audit compliance audits compliance manager compliance reporting conference configuration connect to database cpu Cross Platform custom counters Custom Views customer survey customer testimonials Dark Theme dashboards data analysis Data Analytics data architect data architecture data breaches Data Collector data governance data lakes data lineage data management data model data modeler data modeling data models data privacy data protection data security data security measures data sources data visualization data warehouse database database administration database administrator database automation database backup database backups database capacity database changes database community database connection database design database developer database developers database development database diversity Database Engine Tuning Advisor database fragmentation database GUI database IDE database indexes database inventory management database locks database management database migration database monitoring database navigation database optimization database performance Database Permissions database platforms database profiling database queries database recovery database replication database restore database schema database security database support database synchronization database tools database transactions database tuning database-as-a-service databases DB Change Manager DB Optimizer DB PowerStudio DB2 DBA DBaaS DBArtisan dBase DBMS DDL Debugging defragmentation Demo diagnostic manager diagnostics dimensional modeling disaster recovery Download drills embedded database Encryption End-user Experience entity-relationship model ER/Studio ER/Studio Data Architect ER/Studio Enterprise Team Edition events execution plans free tools galera cluster GDPR Getting Started Git GitHub Google Cloud Hadoop Healthcare high availability HIPAA Hive hybrid clouds Hyper-V IDERA IDERA ACE Index Analyzer index optimization infrastructure as a service (IaaS) infrastructure monitoring installation Integrated Development Environment interbase Inventory Manager IT infrastructure Java JD Edwards JSON licensing load test load testing logical data model macOS macros managed cloud database managed cloud databases MariaDB memory memorystorage memoryusage metadata metric baselines metric thresholds Microsoft Azure Microsoft Azure SQL Database Microsoft PowerShell Microsoft SQL Server Microsoft Windows MongoDB monitoring Monitoring Tools Monyog multiple platforms MySQL news newsletter NoSQL Notifications odbc optimization Oracle PeopleSoft performance Performance Dashboards performance metrics performance monitoring performance schema performance tuning personally identifiable information physical data model Platform platform as a service (PaaS) PostgreSQL Precise Precise for Databases Precise for Oracle Precise for SQL Server Precise Management Database (PMDB) product updates Project Migration public clouds Query Analyzer query builder query monitor query optimization query performance Query Store query tool query tuning query-level waits Rapid SQL rdbms real time monitoring Real User Monitoring recovery regulations relational databases Releases Reporting Reports repository Restore reverse engineering Roadmap sample SAP Scalability Security Policy Security Practices server monitoring Server performance server-level waits Service Level Agreement SkySQL slow query SNMP snowflake source control SQL SQL Admin Toolset SQL CM SQL code SQL coding SQL Compliance Manager SQL Defrag Manager sql development SQL Diagnostic Manager SQL Diagnostic Manager for MySQL SQL Diagnostic Manager for SQL Server SQL Diagnostic Manager Pro SQL DM SQL Doctor SQL Enterprise Job Manager SQl IM SQL Inventory Manager SQL Management Suite SQL Monitoring SQL Performance SQL Quality SQL query SQL Query Tuner SQL Safe Backup SQL script SQL Secure SQL Security Suite SQL Server sql server alert SQL Server Migration SQL Server Performance SQL Server Recommendations SQL Server Security SQL statement history SQL tuning SQL Virtual Database sqlmemory sqlserver SQLyog Storage Storage Performance structured data Subversion Support tempdb tempdb data temporal data Tips and Tricks troubleshooting universal data models universal mapping unstructured data Uptime Infrastructure Monitor user experience user permissions Virtual Machine (VM) web services webinar What-if analysis WindowsPowerShell

Writing SQL queries makes up a significant part of a database administrator’s (DBA) or developer’s job. The ability to write efficient queries can have a dramatic effect on database performance. This post will look at how using basic SQL Server indexes effectively contributes to improved query response time.

How Data is Stored Can Impact Response Time

It’s easy to write slow queries using SQL. You only tell the database what you want without any explicit instructions on how to satisfy the query. Even simple and similar queries can use different execution plans and take substantially different amounts of time to complete. 

The way the data is stored greatly impacts the ability of a database engine to satisfy a query request. Finding records in a database can be accomplished by scanning, seeking, or a combination of both techniques. Using indexes provides a more efficient method of locating specific data elements stored in a database.

How tables are constructed influences the way the database searches for query results. Tables can be structured as a heap in which there is no defined order to its data rows. In some cases, using a heap can be a valid way to store data.

Tables can also have a defined order for data rows and store them based on key values. This structure is known as a Clustered Index (CI) and results in a clustered table. A table can only have one CI. Tables can also have nonclustered indexes which can facilitate finding data elements quickly.

In the vast majority of applications, a clustered index provides more efficient access to specific data elements and improves query performance over using a heap.

Clustered vs Nonclustered Indexes

Indexes are structures associated with a table or view designed to speed data retrieval. The index contains keys built from the table’s columns and is stored in a tree. Traversing the tree to locate data elements leads to better database response.

Two types of indexes are available in SQL Server.

  • Clustered indexes sort and store a table’s data rows based on their key values. Only one clustered index can be created for each table as the rows can only be stored in one order. A clustered table is differentiated from a heap by the existence of a clustered index.
  • Nonclustered indexes have a structure independent of data rows. They contain nonclustered index key values that have a pointer to the data row that stored the key value. 

Both types of indexes can be unique, meaning that there is only one combination that leads to a specific data element.

Writing Queries Using Indexes 

Query response time is directly related to the number of pages that need to be read into memory to satisfy a request. Constructing queries that allow the database engine to take advantage of indexes limits the number of pages that need to be examined to return the appropriate results. 

Following are some tips for writing queries that make efficient use of indexes.

  • Ensure that the columns that will be tested by WHERE, JOIN, and HAVING clauses are in an index.
  • Don’t hide column values so they cannot be used by the index. This includes using functions on column values that make it impossible for them to be used effectively.
  • Primary key constraints and unique key constraints should be used to create indexes for queries whenever possible.
  • Strive to create predicates where SQL Server can isolate a value or range of index key values it needs to process. Most functions and operators inhibit the database engine from using indexes. 
  • Pay attention to the order of the key values in an index so they can be used more efficiently. 
  • Make sure your sort order or GROUP BY statements are supported by the index.

More tips are available in an IDERA webcast that takes a deeper look into how using indexes properly can improve query performance. The video provides many hands-on examples of using indexes in SQL Server and is an excellent source of information for DBAs and developers interested in improving database performance.

A Flexible Tool for DBAs and Developers

Aqua Data Studio is a versatile tool that can be used for a wide range of activities by a database team, including writing queries for SQL Server. In addition to its capacity for tuning queries in SQL Server, it supports performing administrative and development functions on over 40 other database platforms. 

With Aqua Data Studio, users can access and develop queries for all supported database platforms from a unified and intuitive interface. The Visual Query Builder and query analysis tools facilitate the creation of high-performing SQL statements. Users can single-step through code to evaluate variables and identify tuning possibilities. Aqua Data Studio is an excellent choice for database teams tasked with supporting the performance of multi-platform environments.

Try Aqua Data Studio for free!