EverSQL Database Performance Knowledge Base

Question 1

EverSQL Database Performance Knowledge Base

Need Optimized Query which take data from three tables

Three tables

accounts, products, users

Select users id and email from users table where there id are in accounts
Then filter them out from products table where user bought more than 3 products (Need to count users in product table and exclude a user if his count is more than 3).
```
   SELECT id, email
FROM  users 
WHERE id
IN (
SELECT user_id
FROM accounts
WHERE users.id = user_id
)
```

I got all users id and emails, but now I need to filter them out from product table. In product table I have 'product_id' and 'leader_id', which is user id.

I need optimized query, because tables are very big

Answer

How to optimize this SQL query?

The following recommendations will help you in your 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.
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.

Optimal indexes for this query:

ALTER TABLE `accounts` ADD INDEX `accounts_idx_user_id` (`user_id`);

The optimized query:

SELECT
        users.id,
        users.email 
    FROM
        users 
    WHERE
        EXISTS (
            SELECT
                1 
            FROM
                accounts 
            WHERE
                (
                    users.id = accounts.user_id
                ) 
                AND (
                    users.id = accounts.user_id
                )
        )

Question 2

EverSQL Database Performance Knowledge Base

Need Optimized Query which take data from three tables

How to optimize this SQL query?

The optimization process and recommendations:

Optimal indexes for this query:

The optimized query:

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