一、安装步骤

SELECT * 
FROM orders
WHERE shipper_id is NULL

返回结果是一个表格 image.png

2.6 The ORDERS BY Clause

SELECT * 
FROM customers
ORDER BY first_name

image.png

我们也可以倒序排列

SELECT * 
FROM customers
ORDER BY first_name DESC

我们也可以，先按一个字段排序，再按一个字段排序

SELECT * 
FROM customers
ORDER BY state, first_name

当我们从一个表格中，提取列时，我们可以用并非被提取的列，来做sort image.png

我们也可以在选择时候，重新为表格插入一列，并且为之命名

SELECT first_name, last_name, 10 AS points
FROM customers
ORDER BY point, first_name

一个比较复杂一点的例子，用到了的知识点有 Alias、WHERE、ORDER BY、DESC

SELECT *, quantity * unit_price AS total_price
FROM order_items
WHERE order_id = 2
ORDER BY total_price DESC

2.7 The Limit Clause

• 我们只想返回表格的前3行

SELECT * 
FROM customers
LIMIT 3
-- page 1:1- 3
-- page 2: 4-6
-- page 3: 7-9

• 我们只想每页返回3个item

SELECT *
FROM customers
LIMIT 6, 3

这个是跳过开始的6个，只返回最后的3个。

2.8 Inner Joins

SELECT * 
FROM orders
INNER JOIN customers
    ON oders.customer_id = customers.cust_id

SELECT order_id, orders.customer_id, first_name, last_name
FROM orders
JOIN customers 
    ON orders.customer_id = customers.customer_id

如果说，认为需要打多个orders或者customers，过于麻烦，我们可以为orders和customers取别名，比如如下

SELECT order_id, o.customer_id, first_name, last_name
FROM orders o
JOIN customers c
    ON o.customer_id = c.customer_id

2.9 Joining Across Databases

2.10 Self Joins

USE sql_hr; -- 选择特定的数据库
SELECT * 
FROM employees e
JOIN employees m
    ON e.reports_to = m.employee_id

2.10 Joining Multiple Tables