GROUP BY子句

GROUP BY 常用的聚合函数, 可以对数据进行汇总

• 一般与常见的一些函数一起使用, 汇总数据后一般没有办法进行使用
• 使用顺序, SELECT, FROM, JOIN, WHERE GROUP BY, HAVING, ORDER BY, LIMIT

-- 使用聚合函数
-- MAX()
-- MIN()
-- AVG()
-- SUM()
-- COUNT();

SELECT 
	MAX(invoice_total) AS highest,
    MIN(invoice_total) AS lowest,
    AVG(invoice_total) AS average,
    SUM(invoice_total) AS total,
    SUM(invoice_total * 1.1) AS number_of_invoices,
    COUNT(payment_date) AS count_of_payments,
    COUNT(*) AS total_records
FROM invoices
WHERE invoice_date > '2019-07-01';

USE sql_invoicing;
SELECT 
	MAX(invoice_total) AS highest,
    MIN(invoice_total) AS lowest,
    AVG(invoice_total) AS average,
    SUM(invoice_total) AS total,
    COUNT(invoice_total * 1.1) AS number_of_invoices,
    COUNT(payment_date) AS count_of_payments,
    COUNT(DISTINCT client_id) AS total_records
FROM invoices
WHERE invoice_date > '2019-07-01';

SELECT 
	SUM(invoice_total) AS total_sales,
    SUM(payment_total) AS total_payments,
    SUM(invoice_total) - SUM(payment_total) AS what_we_expect
FROM invoices;
-- Exercise
SELECT 
	'First half of 2019' AS date_range,
    SUM(invoice_total) AS total_sales,
    SUM(payment_total) AS total_payments,
    SUM(invoice_total - payment_total) AS what_we_expect
FROM invoices
WHERE invoice_date 
	BETWEEN '2019-01-01' AND '2019-06-30'
UNION
SELECT 
	'Second half of 2019' AS date_range,
    SUM(invoice_total) AS total_sales,
    SUM(payment_total) AS total_payments,
    SUM(invoice_total - payment_total) AS what_we_expect
FROM invoices
WHERE invoice_date 
	BETWEEN '2019-07-01' AND '2019-12-30'
UNION
SELECT 
	'Total' AS date_range,
    SUM(invoice_total) AS total_sales,
    SUM(payment_total) AS total_payments,
    SUM(invoice_total - payment_total) AS what_we_expect
FROM invoices
WHERE invoice_date 
	BETWEEN '2019-01-01' AND '2019-12-30';
    
-- 数据分组
SELECT 
	state,
        city,
	client_id,
	SUM(invoice_total) AS total_sales
FROM invoices i
JOIN clients USING (client_id)
WHERE invoice_date >= '2019-07-01'
GROUP BY client_id
ORDER BY total_sales DESC;

SELECT 
	state,
    city,
	SUM(invoice_total) AS total_sales
FROM invoices i
JOIN clients USING (client_id)
WHERE invoice_date
GROUP BY state, city;

SELECT 
	date,
    pm.name AS payment_method,
    SUM(amount) AS total_payments
FROM payments p
JOIN payment_methods pm 
	ON p.payment_method = pm.payment_method_id
GROUP BY date, payment_method
ORDER BY date;

-- HAVING
SELECT 
	client_id,
    SUM(invoice_total) AS total_sales,
    COUNT(*) AS number_of_invoices
FROM invoices
GROUP BY client_id
HAVING total_sales > 500;

SELECT 
	client_id,
    SUM(invoice_total) AS total_sales,
    COUNT(*) AS number_of_invoices
FROM invoices
GROUP BY client_id
HAVING total_sales > 500 AND number_of_invoices > 5;

-- Exercise
-- Get the customers
-- located in Virginia
-- Who have spent more than 100
USE sql_store;


SELECT 
	order_id,
	first_name, 
    last_name,
    state,
    SUM(quantity * unit_price) AS total_price
FROM customers c
JOIN orders o 
	USING (customer_id)
LEFT JOIN order_items oi
	USING (order_id)
GROUP BY order_id
HAVING state = 'VA' and total_price > 60;


SELECT 
	c.customer_id,
    c.first_name,
    c.last_name,
    SUM(oi.quantity * oi.unit_price) AS total_sales
FROM customers c
JOIN orders o USING (customer_id)
JOIN order_items oi USING (order_id)
WHERE state = 'VA'
GROUP BY
	c.customer_id,
    c.first_name,
    c.last_name
HAVING total_sales > 100;

-- WITH ROLLUP
USE sql_invoicing;
SELECT 
	client_id,
    SUM(invoice_total) AS total_sales
FROM invoices
GROUP BY client_id WITH ROLLUP;

-- 分组,只能在MySQL用
SELECT 
	state,
    city,
    SUM(invoice_total) AS total_sales
FROM invoices i
JOIN clients c USING (client_id)
GROUP BY state, city WITH ROLLUP;

-- Exercise
SELECT 
	pm.name AS payment_method,
    SUM(p.amount) AS total
FROM payments p 
JOIN payment_methods pm 
	ON p.payment_method = pm.payment_method_id
GROUP BY pm.name WITH ROLLUP;

SELECT 
	pm.name AS payment_method,
    SUM(amount) AS total
FROM payments p
JOIN payment_methods pm
	ON p.payment_method = pm.payment_method_id
GROUP BY pm.name WITH ROLLUP;