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 OR Conditions By Using UNION (modified query below): In mosts cases, filtering using the OR operator cannot be applied using indexes. A more optimized alternative will be to split the query to two parts combined with a UNION clause, while each query holds one part of the original OR condition.
- 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: 16): 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:
ALTER TABLE `child` ADD INDEX `child_idx_id` (`id`);
The optimized query:
SELECT
parent_field,
child_field
FROM
((SELECT
parent.field AS parent_field,
child.field AS child_field
FROM
parent
JOIN
child
ON (
child.id = parent.otherid
))
UNION
DISTINCT (SELECT
parent.field AS parent_field,
child.field AS child_field
FROM
parent
JOIN
child
ON (child.id = parent.id))
) AS union1