How to optimize this SQL query?
In case you have your own slow SQL query, you can optimize it automatically here.
For the query above, the following recommendations will be helpful as part of the SQL tuning process.
You'll find 3 sections below:
- Description of the steps you can take to speed up the query.
- The optimal indexes for this query, which you can copy and create in your database.
- An automatically re-written query you can copy and execute in your database.
The optimization process and recommendations:
- Avoid Correlated Subqueries (query line: 13): A correlated subquery is a subquery that contains a reference (column: Date) to a table that also appears in the outer query. Usually correlated queries can be rewritten with a join clause, which is the best practice. The database optimizer handles joins much better than correlated subqueries. Therefore, rephrasing the query with a join will allow the optimizer to use the most efficient execution plan for the query.
- Avoid Subqueries (query line: 5): We advise against using subqueries as they are not optimized well by the optimizer. Therefore, it's recommended to join a newly created temporary table that holds the data, which also includes the relevant search index.
The optimized query:
Minutes = SUM(r.MinutesRead),
Pages = SUM(r.PagesRead)
r.Date >= @p0) r0 CROSS APPLY (SELECT
TOP 1 r.MinutesRead,
r0.Date = r.Date
AND r0.UserId = r.UserId
AND r0.UserGroupId = r.UserGroupId
AND r0.BookId = r.BookId
AND r.Date >= @p0
r.PagesRead DESC) r