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: 4): A correlated subquery is a subquery that contains a reference (column: inscode) 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 Selecting Unnecessary Columns (query line: 2): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
The optimized query:
SELECT
*
FROM
fs_export_stage_data_customer m CROSS APPLY (SELECT
count(*)
FROM
fs_export_stage_data_customer m2
WHERE
m2.inscode = m.inscode) sq1(cnt)
INNER JOIN
fs_export_stage_session se
ON m.session = se.id
WHERE
cnt > 1
ORDER BY
m.inscode,
m.comb_dbupddate