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:
- 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.
- Use UNION ALL instead of UNION (query line: 9): Always use UNION ALL unless you need to eliminate duplicate records. By using UNION ALL, you'll avoid the expensive distinct operation the database applies when using a UNION clause.
Optimal indexes for this query:
CREATE INDEX test_idx_category ON test (category);
The optimized query:
SELECT
test.category,
test.timefield
FROM
test
WHERE
test.category = 'A'
UNION
SELECT
TOP 10 test.category,
test.timefield
FROM
test
WHERE
test.category = 'B'
ORDER BY
timefield DESC