EverSQL Database Performance Knowledge Base

The optimization process and recommendations:

1. 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.
2. Replace In Subquery With Correlated Exists (modified query below): In many cases, an EXISTS subquery with a correlated condition will perform better than a non correlated IN subquery.
3. Use Numeric Column Types For Numeric Values (query line: 15): Referencing a numeric value (e.g. 1) as a string in a WHERE clause might result in poor performance. Possible impacts of storing numbers as varchars: more space will be used, you won't be able to perform arithmetic operations, the data won't be self-validated, aggregation functions like SUM won't work, the output may sort incorrectly and more. If the column is numeric, remove the quotes from the constant value, to make sure a numeric comparison is done.

Optimal indexes for this query:

ALTER TABLE `checkin_request_ticket` ADD INDEX `checkin_ticket_idx_salvage_part_checkin_id` (`salvage_part`,`checkin_id`);
ALTER TABLE `invoice` ADD INDEX `invoice_idx_invoice_id` (`invoice_id`);

The optimized query:

SELECT
        s.sales_id,
        s.pid,
        s.quantity,
        IFNULL((SELECT
            i.invoice_id 
        FROM
            invoice AS i 
        WHERE
            NOT EXISTS (SELECT
                1 
            FROM
                checkin_request_ticket AS crt 
            WHERE
                (crt.salvage_part = '1') 
                AND (i.checkin_id = crt.checkin_id)) 
            AND i.invoice_id = s.sales_id), s.quantity) AS checkquan 
    FROM
        sales AS s