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 In Select Clause (modified query below): The aggregation function located in a subquery inside the SELECT clause, is executed once for every matched row. Extracting this subquery to a temporary table will improve performance significantly.
- Avoid Optimizer Hints (modified query below): Using optimizer hints such as FORCE INDEX can be valuable in the short term. When important aspects such as the amount of data or the data distribution change, these hints can do more harm than good.
- Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.
Optimal indexes for this query:
ALTER TABLE `ReaderFeedback` ADD INDEX `readerfeedback_idx_parentfeed_approved_date` (`ParentFeedbackId`,`Approved`,`Date`);
ALTER TABLE `es_temp1` ADD INDEX `es_temp1_idx_emailaddress` (`EmailAddress`);
The optimized query:
ON es_temp1.EmailAddress = ReaderFeedback.EmailAddress
ReaderFeedback.ParentFeedbackId = 123
AND ReaderFeedback.Approved = 1