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 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.
- Avoid Subqueries (query line: 4): 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.
- Avoid Subqueries (query line: 13): 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.
- 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.
- Push Filtering Conditions Into Subqueries (modified query below): Parts of the WHERE clause can pushed from the outer query to a subquery / union clause. Applying those conditions as early as possible will allow the database to scan less data and run the query more efficiently.
Optimal indexes for this query:
ALTER TABLE `Dual` ADD INDEX `dual_idx_rownum` (`Rownum`);
ALTER TABLE `Table_Name` ADD INDEX `table_name_idx_rowid_seq_number` (`Rowid`,`seq_number`);
ALTER TABLE `User_Tab_Columns` ADD INDEX `user_columns_idx_table_name_column_name` (`Table_Name`,`Column_Name`);
The optimized query:
SELECT
X1.*
FROM
(SELECT
Dual.Rownum seq_number
FROM
Dual
WHERE
(
Dual.Rownum <= 10
) CONNECT
BY
Dual.Rownum <= (SELECT
LPAD(9,
(UTC.DATA_PRECISION - UTC.DATA_SCALE),
9)
FROM
User_Tab_Columns UTC
WHERE
UTC.Table_Name = 'Table_Name'
AND UTC.Column_Name = 'seq_number')) X1,
Table_Name X2
WHERE
X1.seq_number = X2.seq_number(+)
AND X2.Rowid IS NULL
AND 1 = 1