Top 21 Ways To Optimize SQL Queries

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Not just 1 but 21!

We know that you were very stressed regarding the optimization of your SQL query. So here we are with the solution to your problem. In this blog, we are going to discuss 21 ways in which you can optimize your SQL query.

We suggest you read the entire article to tune the performance of your SQL query.

Top 21 Ways to Optimize SQL Queries

1. Identify and add missing indexes

Identifying and adding missing indexes is one of the most important tips for optimizing SQL queries. The table indexes in the SQL database contribute to retrieving information effectively and efficiently.

When you run a query in SQL Server, the generator optimizes it and generates an execution plan. In this case, the missing index that was created to optimize the query may be detected. As a result, the execution plan will suggest your query in the warning section. Through this, you will be informed about the appropriate columns in which the current SQL should be indexed. Hence, this will result in improved performance.

An alternate way of identifying missing indexes is to analyze the graphical query plan.

2. Try to identify unused indexes

You may experience situations where there are indexes present, but they are not being used. One reason behind this may be implicit data type conversion. Hence, to optimize your SQL query, you need to identify the unused indexes.

Sometimes the SQL Server performs implicit data type conversion while you execute your query. The SQL Server runs the comparison only after it converts the data into varchar. Hence, in this case, indexes, won’t be used. Well, don’t panic; we have the solution to your problem. We recommend you use the CAST function. The CAST function is capable of converting a value into any particular data type.

3. Try to avoid using multiple OR in the FILTER predicate

There are situations where you would like to combine two or more conditions. In this case, we recommend you avoid using the OR operator. Also, try to eliminate splitting the query into different parts, as it may lead to separating search expressions. This is one of the most important points to keep in mind while optimizing your SQL query.

The SQL Server is not capable of processing the OR operator within one operation. In fact, it evaluates each component of the OR. Hence, it may result in poor performance.

Don’t worry; we have a solution to this as well. Consider splitting a particular query into two SELECT queries. Now use the UNION operator to combine them. By doing this, the SQL Server will be able to use indexes. As a result, your SQL query will be optimized.

4. Try to use wildcards only at the end of a phrase

Wildcards serve as placeholders for the words and phrases that can be added at the beginning or the end of them. Wild cards can be used at both the beginning and the end of a phrase. Moreover, to optimize your SQL query, you should add the wild cards only at the end of a phrase. This also facilitates efficient and effective retrieval of data. As a result, your query will retrieve the exact answer to your question.

We would also advise you to create a persistent computed column. This will help you in situations where you will have to search by the last symbol of a word, number, or phrase. You should also consider using the REVERSE function on it to speed up the back search.

5. Try to avoid too many JOINs

To optimize your SQL query, you should avoid having too many JOINs.

You may end up overloading your query by adding multiple tables and joining them up. While generating a plan, the SQL optimizer needs to apply filters and aggregation to the tables. For this, he needs to identify how the tables are joined and in what order they are joined. Hence, the more tables you have, the more perplexing your query becomes. As a result, the SQL server may generate an inefficient execution plan.

The most effective solution is to split a single query into several queries. You may later join these several queries. But at present, this will help you remove unnecessary joins, subqueries, tables, etc. You may consider using this technique, as it is great for achieving efficient query plans.

6. Try to avoid using SELECT DISTINCT

The SQL SELECT DISTINCT operator is used to select only particular and unique values of the column. It mainly focuses on eliminating duplicate values. Moreover, the SQL server requires a tool to process large volumes. As a result, the query is processed at a comparatively low speed. Hence, to avoid this, we would recommend that you avoid using SELECT DISTINCT. Instead, try specifying columns by simply running the SELECT statement. This will undoubtedly aid in the optimization of your SQL query.

7. Use SELECT fields instead of using SELECT *

To optimize your SQL query, try using SELECT fields instead of SELECT *.

You may be familiar with the function of the SELECT statement. It is mainly used to retrieve data from the database. There are situations when the database is huge. In situations like these, we recommend you not retrieve all the data. Retrieving a huge amount of data may require a lot of additional resources for working on the query.

In the event that you decide to retrieve a huge amount of data, the result table may be loaded with a lot of data. It will also require a lot of memory and CPU usage. An alternative to this is that you can specify the exact columns from which you need to get the data. In this case, the resources of the database will also be saved. Additionally, the query will have a lower cost as the SQL Server will only retrieve the required data.

There may be situations in which you need to retrieve data regularly. It can be for any specific purpose, maybe authentication or verification. In this case, we recommend using covering indexes. Their biggest advantage is that they contain all the fields required by the query. Hence, they help in improving your query performance. In addition, they guarantee better results.

8. Try to use TOP to sample query results

You may be familiar with the function of the SELECT TOP statement. It is mainly used to set a limit on the number of records that can be returned from a database.

To ensure that your query produces the desired results, you can use the SELECT TOP command. This will definitely help you optimize your SQL query. In addition, the SELECT TOP command can also be used to fetch several rows as a sample.

9. Try running the query during the off-peak hours

This is one of the main points that you can consider for optimizing your SQL query. Try to schedule the execution of your SQL query during off-peak hours. It is the best time to optimize your SQL query.

There may be times when you need to run multiple SELECT queries, execute complex queries with nested subqueries, or loop queries. In all these situations, running your SQL query during off-peak hours is the best decision you can make.

Consider a situation in which you are running a heavy query against the SQL database.  In this case, the SQL Server will lock the tables on which you are working. This is done to eliminate the concurrent use of resources through different transactions. This clearly indicates that the other users will not be able to work on those particular tables.

Now, considering the above situation/example, we would recommend avoiding executing heavy queries during peak hours. It will clearly result in server overload. Additionally, it will also restrict other users from accessing a particular amount or portion of data.

An alternative mechanism to avoid this problem is to use the WITH (NOLOCK) hint. The NOLOCK hint, as its name implies, allows users to retrieve data without being affected by any kind of lock.

Everything has its advantages and disadvantages. The same goes for the NOLOCK hint as well. By using the NOLOCK hint, the user may be subjected to working with dirty data. This is one of the major drawbacks of the NOLOCK hint. In this case, we recommend that you use snapshot isolation. It will help in avoiding data locking by making use of row versioning. In fact, it guarantees a consistent snapshot of each transaction going on in the database.

10. Try to minimize the usage of any hint regarding the query

It is very common for people to use query hints when they face performance issues. According to them, these query hints help optimize the search query. Using query hints encourages the optimizer to generate an execution plan based on the same hint.

Query hints generally include the Optimize For, Recompile, and NOLOCK commands. However, they may cause unexpected side effects, undesirable impacts, or even break business logic when trying to solve the query. As a result, you should consider limiting the use of any query-related hint.

Additionally, make sure that you always monitor, check, manage, and keep the hints up to date.

11. Try to minimize large write operations

Actions like writing, modifying, deleting, or exporting a large amount of data may adversely impact your query performance. Hence, to optimize your SQL query, you need to minimize large write operations.

In addition, it may also block the table when a modification or manipulation of data is required. Adding indexes, checking constraints on the queries, and processing triggers are also not possible if the table is blocked. Also, another drawback of writing a lot of data is that it will increase the size of the log files.

Even after considering all the above points, large write operations are still not a very huge performance issue. But we would still recommend you use them in moderation. Stay aware of the consequences that can occur. Also, be ready for any unexpected behaviour.

Additional Tips

Try using file groups to distribute data across multiple physical discs. This is indeed one of the best practices for effectively optimizing SQL Server performance. This trick helps facilitate multiple write operations simultaneously and effectively.

You can try compression and data partitioning as well. It will minimize the cost of large write operations. Hence, this will surely help you optimize your SQL query.

12. Try to create JOINs with INNER JOIN

The INNER JOIN statement tends to return all the similar rows from the joined tables. On the other hand, the WHERE clause separates the resulting rows based on particular conditions. This process of retrieving data from multiple tables using the WHERE clause is called NON-ANSI JOINs. On the other hand, the INNER JOIN belongs to ANSI JOINs.

You can write your query in whatever way you want. You may use ANSI JOINs or NON-ANSI JOINs. It hardly makes a difference for the SQL Server. But the thing is, it gets very easy to understand and analyze the query if you use ANSI JOINs. The JOIN conditions and the WHERE filter can be clearly located. You can also double-check to see if you missed any join or predicate filters or whether you joined the required tables or not.

13. Try to use LIMIT to sample query results

We know that your main aim is to optimize your SQL query to get the desired results. As a result, we recommend you use the LIMIT statement to obtain appropriate, meaningful, and desirable results.

The LIMIT statement returns only particularly specified records. Hence, by using a LIMIT statement, you can prevent taxing the production database by using a large query. As a result, your SQL query will be optimized.

Note: In some DBMS systems, the word “LIMIT” is interchangeably used with the word “TOP.”

14. Try to secure your code

This point may be very strange for you. You may be wondering how securing your code will aid in SQL query optimization. Well, read the above paragraph to understand this point.

As you may be aware, databases store a massive amount of diverse data. As a result, they make an excellent primary target for hackers. Some users enter their SQL query instead of their username in the SQL injections. This SQL injection attacks the user’s database by retrieving or modifying the data. It is, moreover, a very common attack.

Do not worry; we have a solution for avoiding the SQL injection attack as well. Try utilizing parameterized statements, input validations, and input sanitization, among other things. This will protect your database from the SQL injection attack.

The DBMS finds out how you secure your database. Hence, focus on understanding the database management system and its security issues.

15. Try using fully qualified database object names

Try to fully qualify the database object names. This intends to eliminate vagueness, resulting in an optimized SQL query.

You may be accessing numerous databases, schemas, and tables. In situations like these, it is very difficult to declare what you want to access. Hence, we recommend you use fully qualified database object names. It will prevent confusion from happening, resulting in an optimized SQL query.

16. Try using the Command SET NOCOUNT ON

Optimize your SQL query by using the Command SET NOCOUNT ON.” Consider using the Command SET NOCOUNT ON, especially while performing INSERT, DELETE, SELECT, and UPDATE operations.

You may be aware that SQL provides the number of affected rows for the procedures of INSERT, DELETE, SELECT, and UPDATE. It may therefore result in low speed when you have complex queries with lots of joins.

By using the Command SET NOCOUNT ON, SQL will not count the impacted rows. As a result, your performance will be increased and improved, and your SQL query will be optimized.

17. Use IN and EXIST Clauses

Avoid utilizing only the IN operator clause while creating a SQL query. Instead, focus on optimizing both the IN and EXIST clauses for complete optimization of your SQL query.

18. Try selecting the appropriate data type

You may be aware that each table column in SQL has a separately associated datatype. Data types such as varchar, text, boolean, integers, dates, etc. are available over there. Hence, in order to optimize your SQL query, it is very important for you to select the appropriate data type.

In addition, selecting the appropriate data types is also very important for various indexing purposes.

19. Try to reduce the number of tables

In order to optimize your SQL query, you can try reducing the number of tables.

Just like any relational query optimizer, the SQL query optimizer server also faces the same problem. The SQL query optimizer server is also subjected to finding an appropriate execution plan. It has to choose out of all the available options, and that too in a very short span of time. It can be equated to the game of chess. Every move after move needs to be evaluated.

During this evaluation process, the SQL query optimizer mainly performs one of these two actions. It will either group plans that are similar or plans that are suboptimal. Or else, it will set aside one plan, considering it a candidate plan.

More tables will directly mean more workload for the SQL query optimizer. There will be endless options available with the SQL optimizer. This will result in an increased workload as there will be a lot of options to choose from. But on the other hand, the SQL optimizer will have limited time to finalize the plan for execution.

Having more tables is not a very big problem. SQL Optimiser will always generate the best plan it can. But clearly, each additional table added to the query will increase its complexity. Hence, by adding more tables, you will just increase the risk of inefficient plans being generated.

Therefore, we suggest that you reduce the number of tables in order to optimize your SQL query.

20. Try to appropriately define your business requirements

In order to completely optimize your SQL query, you should focus on appropriately defining your business requirements.

You need to have a proper understanding of the requirements of your business. Here are some practices that you can consider for defining your business requirements.

  1. Try to identify the relevant stakeholders of your business
  2. Focus on the outcomes generated by your business
  3. Identify the intended audience of your business
  4. Optimise the requirements before framing the discussion
  5. Focus on asking appropriate and relevant questions
  6. Focus on particular requirements and discuss them with the stakeholders

All these practices will help you focus on your business requirements. Hence, you can consider them while optimizing your SQL query.

21. Use WHERE Command instead of HAVING Command, to define filters

We recommend you define filters using the WHERE command rather than the HAVING command. This will be a great way to optimize your SQL query.

We expect our query to return the desired results from the database. This is the reason we focus on optimizing it. Also, the primary goal of putting up an optimized query is to pull only the required records from the database.

Did you know that HAVING statements are calculated after WHERE statements? Well, this is according to the SQL Order of Operations. Hence, it will be more efficient to use the WHERE statement for filtering a query based on conditions.

Conclusion

This was all about the top 21 ways to optimize your SQL query. We tried our best to cover all the ways available for optimizing the SQL query. This blog definitely contains a lot of fine tips and techniques that will help you improve your performance while executing your SQL query. 

We sincerely hope that these tips and techniques assist you in improving your performance and avoiding any potential problems.

Please let us know your viewpoints in the comment section. We are open to appreciation and improvement as well. We will be more than happy to hear from you.

Looking For SQL Certification for you or your employees? Kindly Connect at partner@edu4sure.com or call us at +91-9555115533.

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