Database performance is determined by several factors and query performance is one of them. SQL performance measures the time it takes to perform a required function and if outcome expectations are met. Improving SQL query performance will have a significant impact on the performance of your database and these are tips any IT consulting service expert would recommend to improve SQL query performance.

1. Schema name: When improving SQL query performance, an IT consulting company will prefix object names, for instance, a stored procedure name, with its schema name. This is done because the SQL server’s engine will attempt to find the object in all schemas until it locates it, which can take time. However, if the schema name is also included in the query, the server engine will not look beyond the schema.
2. Use of * in select statements: When you enter an * in column names, the server scans all column names and replaces the * with the column names of the tables in the SQL select statement. This search and replace process can slow down the performance of the SQL query, which is why you should use column names instead of a * in column names. Hosting services can be enhanced by making this simple change to your queries.
3. EXISTS instead of IN: When you enter IN in a SQL query, the server will collect all the data of the subquery first. This is faster only if your subquery is very small. However, when your subquery is large, using IN can slow down SQL query performance. It is thus faster to use EXISTS, which will return true if a subquery contains any rows.
4. NOT EXISTS instead of NOT IN: If you use NOT IN in your query, the server will check every single result to see if it is null. This happens even if the query does not return rows with null values and can impact performance negatively. However, when you use NOT EXISTS in the query instead, you can enhance performance as the server will not check each result to see if it is null.
5. Table variables: IT service management looks at different ways to improve SQL query performance. While the above mentioned methods are useful, an IT consulting service expert may recommend that you do not use table variables in joins. You may instead use temporary tables, common table expressions or CTEs, or derived tables.
6. Using table variables in joins can reduce performance speeds because the server engine will see the table variables as a single row. On the other hand, temporary tables, CTEs, and derived tables perform better with joins.
7. Join type: It is also important to use a proper join type and join order. An inner join’s function is to select all rows from both tables as long as there is a match between the columns. The outer join will return all matching records from both tables whether or not the other table matches.
8. Stored procedure names: When improving your SQL query performance, you should avoid starting your stored procedure name with sp_ or SP_. This is because the server will always check the system or master database even if the schema name is provided if the stored procedure name begins with sp_ or SP_. When you use a name that does not begin with either, the server will eliminate an unnecessary process, thus enhancing performance.
9. SET NOCOUNT ON: An SQL server performing DML operations like select, insert, delete, and update will always return the number of rows affected. Hosting services consider this to have a significant impact on performance in complex queries with a lot of joins. By using SET NOCOUNT ON in DML operations, the server will not count the number of rows affected.
10. Stored procedure: A stored procedure, by default, is precompiled. This means that the stored procedure is compiled when it executes for the first time, creating an execution plan for subsequent calls, and the query processor will not be required to create a new plan.

Using stored procedure for a complex or frequently used query is thus another way of improving your SQL query performance.

Related Articles