How to use SQL statements to perform complex data calculations and processing in MySQL?

MySQL is a popular relational database management system. It not only provides basic data operation functions, but also supports complex data calculation and processing. This article will introduce how to use SQL statements to perform complex data calculations and processing in MySQL, and provide specific code examples.

1. Use aggregate functions for data calculation

MySQL provides a set of aggregate functions for calculating a set of data to obtain a summary result. Commonly used aggregate functions include: SUM, AVG, MIN, MAX, COUNT, etc. Here are examples of data calculations using these aggregate functions:

1.1 Calculate the total amount of all orders

SELECT SUM(total_price) AS total_sum FROM orders;

1.2 Calculate the average amount of all orders

SELECT AVG(total_price) AS avg_price FROM orders;

1.3 Calculate the maximum order Amount and corresponding customer ID

SELECT MAX(total_price) AS max_price, customer_id FROM orders GROUP BY customer_id ORDER BY max_price DESC LIMIT 1;

2. Use subquery for data processing

Subquery is a query statement nested in another SQL statement, which can process data Grouping processing, filtering and calculation. The following is an example of using subqueries for data processing:

2.1 Calculate the latest order amount of each customer

SELECT customer_id, total_price 
FROM orders 
WHERE (customer_id, created_at) IN (SELECT customer_id, MAX(created_at) FROM orders GROUP BY customer_id);

2.2 Delete customers whose total order amount is less than 100

DELETE FROM customers WHERE id IN (SELECT DISTINCT customer_id FROM orders GROUP BY customer_id HAVING SUM(total_price) < 100);

3. Use joint table query for multi-table data processing

Joint table query is to connect multiple tables according to related fields to obtain related data sets. Joint table queries can merge, filter and calculate data. The following is an example of using joint table query for multi-table data processing:

3.1 Calculate the total order amount and total payment amount of each customer

SELECT customers.id, customers.name, SUM(orders.total_price) AS total_order_sum, SUM(payments.amount) AS total_payment_sum 
FROM customers 
LEFT JOIN orders ON customers.id = orders.customer_id 
LEFT JOIN payments ON customers.id = payments.customer_id 
GROUP BY customers.id;

3.2 Find those who have placed more than two orders at the same time Customer

SELECT customer_id FROM orders GROUP BY customer_id HAVING COUNT(*) >= 2;

This article introduces how to use SQL statements to perform complex data calculation and processing in MySQL, including the use of aggregate functions, subqueries, joint table queries and other technologies. Through these technologies, we can process large-scale database data more efficiently and obtain the required results.

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