When it comes to reducing the response time in web projects, various developers avoid optimizing the servers. This negligence is the result of developers bringing changes at the outer level or focusing on the index existence of database columns. The problem with this behavior is that developers focus on something perfect while they ignore the only thing that could improve the performance or response time of web applications, i.e. SQL servers.
While improving the associated elements can greatly impact the working of any application, finding and targeting areas that are in dire need of improvement can be a life-saver. Developers and design architects need to understand that improving queries for SQL servers can result in improved performance. Considering its importance, here are a few tips that will help optimize SQL server queries.
1. The use of * operator
When it comes to SELECT statements, always prefer column names instead of using * operator. The reason behind this action is that the SQL servers scan column names and if there is any * it will be replaced with the column names available in the table regarding the SQL SELECT statement.
Providing the machines with suitable column names ensures that this action of replacing does not take place. This step is necessary for improving performance.
2. Use WHERE and not HAVING to define filters
The main goal of any query is to pull out the record or history from databases that are relevant to the question. According to the Order of the SQL Operations, WHERE statements are calculated before HAVING statements.
If the user’s intent behind the query is to filter out certain conditions, a WHERE statement will serve the purpose better. On the other hand, a HAVING statement will be well-suited to such conditions where the filtering is achieved through an aggregated field.
3. Schema/Owner name
Stored procedure or table name must be written after the schema/owner name. In the absence of schema/owner name in the prefix, SQL servers will fail to find it immediately and will have to browse through all the schemas to find the object (stored procedure or table name). On the flip side, if the owner/schema name is available, SQL servers will not browse the tables outside of the marked schema name.
4. Keep wildcards for a phrase’s end only
Wildcards broaden the search perimeter when plaintext data like names or cities are involved. The only downside to this strategy is that the wider the perimeter, the difficult it becomes to search for data quickly.
Developers often make the mistake of combining leading wildcard with an ending wildcard to search the databases. However, the presence of wildcard (%) before and after search queries fetches irrelevant results from the databases. Because of this, developers must stick with using a wildcard only at the end to narrow the search perimeter.
5. Nullable columns
With nullable columns, it is better to use NOT EXISTS action instead of using NOT IN. When opting with the latter option in any query, the SQL servers browse through every table or column to check if it is null or not.
Preferring NOT EXISTS action in any query would allow the SQL servers to not compare the results with nulls. This course of action will save time.
6. Refrain from using ORDER BY, DISTINCT, and GROUP BY
GROUP BY, ORDER BY, and DISTINCT; a search query conducted in this order will not generate desired results. The reason is that, in this particular order, the SQL servers put the data on work tables that are created as a result of the execution of the above-mentioned query.
Since this query deviates from the actual action, creates unnecessary data, and consumes time, it is better to use it only in dire circumstances.
7. Joins and Table Variables
Refrain from using table variables in join. Instead, make use of Common Table Expressions (CTEs), derived tables or temporary tables in join.
Although table variables are extremely efficient and fast in various situations, they are viewed as a singular row by the SQL servers. Because of this, table variables tend to perform badly when combined with joins. Derived tables or CTEs provide a better option when it comes to joins because of which they must be preferred with it.
8. Procedure names with sp_
Developers often make the mistake of beginning their procedure name queries with sp_. This action is careless since it compels SQL servers to browse through the entire database even if the action contains the schema/owner name.
Supplying the SQL servers with procedure names without sp_ will reduce the number of unnecessary checks within the main database.
Additional Tips
• Never utilize cursors within queries.
• The majority of the time, it is better to use UNION ALL to make several queries. Instead of making unique queries with OR operations, stick with the above-mentioned action.
• Always limit the columns and rows of your result. In this way, you can save memory, network, and disk of the SQL server. Just keep in mind to use TOP and verify the WHERE clause whenever necessary.
• Avoid depending on joins in your query too much and only use it when necessary.
• Use SET NOCOUNT ON when it comes to complex queries that have various joins. This action will improve the overall performance as it does not count the affected rows.
• When you have a choice between using BETWEEN and IN clause, always prefer the former choice as it serves in a better way.
• Refrain from using the SUBSTRING action in the queries.
Conclusion
With this, we conclude the article. Although this topic is a bit complicated in nature, we hope the optimizations tips that we have provided will help you understand the SQL server concepts in a better way. The most important thing to learn from this article is the optimization tips (obviously) and how one can use them to work out the nuisances associated with the tables, indexes, and database objects in your PHP software development projects.
Once you have figured out how everything works and which course of action is suitable for different situation, query optimization of SQL servers will seem simple and fun!