像Excel一样使用SQL进行数据分析（下）

2022-04-29 22:10:09

排名

数值相同的排名相同且排名连续

SELECT prod_price,
(SELECT COUNT(DISTINCT prod_price)
FROM products
WHERE prod_price>=a.prod_price
) AS rank
FROM products AS a
ORDER BY rank ;

5 字符串处理

字符串替换

UPDATE data1 SET city=REPLACE(city,'SH','shanghai');
SELECT city FROM data1;

按位置字符串截取

字符串截取可用于数据分列

MySQL 字符串截取函数：left(), right(), substring(), substring_index()

SELECT left('example.com', 3);

从字符串的第 4 个字符位置开始取，直到结束

SELECT substring('example.com', 4);

从字符串的第 4 个字符位置开始取，只取 2 个字符

SELECT substring('example.com', 4, 2);

按关键字截取字符串

取第一个分隔符之前的所有字符，结果是www

SELECT substring_index('www.google.com','.',1);

取倒数第二个分隔符之后的所有字符，结果是google.com;

SELECT substring_index('www.google.com','.',-2);

6 筛选

通过操作符实现高级筛选

使用 AND OR IN NOT 等操作符实现高级筛选过滤

SELECT prod_name，prod_price FROM Products
WHERE vend_id IN('DLL01','BRS01');
SELECT prod_name FROM Products WHERE NOT vend_id='DLL01';

通配符筛选

常用通配符有% _ [] ^

SELECT * from customers WHERE country LIKE "CH%";

7 表联结

SQL表连接可以实现类似于Excel中的Vlookup函数的功能

SELECT vend_id,prod_name,prod_price
FROM Vendors INNER JOIN Products
ON Vendors.vend_id=Products.vend_id;
SELECT prod_name,vend_name,prod_price,quantity
FROM OderItems,Products,Vendors
WHERE Products.vend_id=Vendors.vend_id
AND OrderItems.prod_id=Products.prod_id
AND order_num=20007;

自联结在一条SELECT语句中多次使用相同的表

SELECT c1.cust_od,c1.cust_name,c1.cust_contact
FROM Customers as c1,Customers as c2
WHERE c1.cust_name=c2.cust_name
AND c2.cust_contact='Jim Jones';

8 数据透视

数据分组可以实现Excel中数据透视表的功能

数据分组

group by 用于数据分组 having 用于分组后数据的过滤

SELECT order_num,COUNT(*) as items
FROM OrderItems
GROUP BY order_num HAVING COUNT(*)>=3;

交叉表

通过CASE WHEN函数实现

SELECT data1.city,
CASE WHEN colour = "A" THEN price END AS A,
CASE WHEN colour = "B" THEN price END AS B,
CASE WHEN colour = "C" THEN price END AS C,
CASE WHEN colour = "F" THEN price END AS F
FROM data1

注：以上代码在MySQL数据库中执行

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