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12 Tips to Write Efficient SQL Queries

  • Difficulty Level : Medium
  • Last Updated : 29 Jun, 2021

We all know the importance of a database in any application. This is the place where a users’ information gets stored and retrieved as per the requirements. SQL is the most popular query language which allows you to store and retrieve data from the database and perform operations. The performance of the database matters a lot when it comes to choose a database and write the queries for a specific task/operation. 

12-Tips-to-Write-Efficient-SQL-Queries

In development, writing the queries is not just important. It is also important to write efficient SQL queries. Efficient queries give faster results. When the SQL queries are optimized your application’s faster performance saves a lot of time. It becomes convenient for both database administrators and for SQL developers as well. You should have a fast SQL server to achieve fast, efficient, and credible database queries. 

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In this blog, we are going to discuss some rules that will help you to make your SQL faster and efficient. 



1. Create Small Batches of Data for Deletion and Updation

Instead of deleting and updating data in bulk create small batches of them. In case if there will be a rollback, you will avoid losing or killing your data. It also enhances concurrency, because the data you except the part you’re deleting or updating continue doing other work. 

2. Use CASE instead of UPDATE

While writing SQL queries UPDATE statement writes longer to a table in comparison to the CASE statement, because of its logging. Inline CASE statement chooses what is preferred before writing it on the table, which eventually increases the speed. 

3. Use Temp Tables

Temporary tables are used in many situations, such as joining a small table to a larger one. You can improve data performance by extracting data from the large table, and then transferring it to a temp table then join with that. This reduces the power required in processing. 

4. Avoid Using Another Developer’s Code

When you use someone else code, there will be a high chance of pulling more data than you need. Cutting down this data may be hard for you but if you trim this code as per your need, you won’t end up with huge data clusters. 



5. Avoid Negative Searches

Negative searches slow down your DB performance a lot. To avoid this, you can re-write the queries with better indexes, especially when you’re dealing with large amounts of data.

6. Use The Exact Number of Columns

While writing the select statement, make sure that you’re writing the correct number of columns against as many rows as you want. This will make your query faster, and you will speed your processes. 

7. No Need to Count Everything in the Table

To check the existence of some data, you need to carry out an action. People often try this:

SET @CT = (SELECT COUNT (*) FROM dbo.T1);If @CT > 0BEGIN <Do something>END

Writing the above statement is unnecessary and it just wastes a lot of time. Instead of the above statement, you can write the statement given below…

If EXISTS (SELECT 1 FROM dbo.T1)BEGIN<Do something>END

From the above method, you can avoid counting every item on the table. When you use EXIST, the SQL server recognizes it and gives faster results. 

8. Avoid Using Globally Unique Identifiers

For ordering the table data, avoid using GUIDs as much as you can. GUID’s can easily fast break off your table. You can use IDENTITY or DATE for dramatic breakoff that takes only a couple of minutes.



9. Avoid Using Triggers

Triggers are not important to use in SQL queries. Whatever you plan to do with your data, go through the same transactions as the previous operations. Using triggers results in lock many tables until the trigger completes the cycle. You can split the data into several transactions to lock up certain resources. This will help you in making your transaction faster. 

10. Avoid Using ORM

Using ORM (Object Relational Mapper) will give you the worst code in the world of technology. You will come across a bad performance in your daily encounters.  If you are unable to avoid them completely, minimize them by writing stored procedures, that are completely your own, and have ORM use yours instead of those it creates. 

11. Avoid Using Distinct Keyword

You should always try to avoid using the DISTINCT keyword. Using this keyword requires an extra operation. This will slow down all the queries and makes it almost impossible to get what you need. 

12. Use Fewer Cursors

Cursors generate many problems, especially on speed. Also, they are the reasons for blockages as well. One operation can block the other operations. This may affect your system concurrency, slowing everything down. 

Conclusion

We have discussed mainly twelve tips for writing efficient SQL queries. It’s not limited here. You can use stored procedures for better efficiency. Also, you can separate large and small transactions. Count your rows using the system table and reduce the nested views to reduce lags. These tips are quite helpful in improving the performance of your SQL server. 

As you will progress in writing more database queries, you will learn how things or queries can be optimized more. Seeing the other developers’ code also helps in writing efficient queries. Hope all these tips are helpful in writing better SQL queries. 

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