一.聚合函数
1.计数函数 COUNT( )
image.png
SELECT COUNT(1) FROM milk_tea AS m;
SELECT COUNT(m.prod_name) FROM milk_tea AS m;
SELECT COUNT(m.pro_date) FROM milk_tea AS m;
SELECT COUNT(m.sale_price) FROM milk_tea AS m;
SELECT COUNT(DISTINCT m.sale_price), COUNT(DISTINCT m.pro_date) FROM milk_tea AS m;
SELECT DISTINCT m.sale_price FROM milk_tea AS m;
image.png
image.png
2.求和函数 SUM
SELECT SUM(m.in_price) FROM milk_tea AS m; ---78.5
SELECT SUM(m.in_price * 1.1) FROM milk_tea AS m; ---86.35
SELECT SUM(m.sale_price) FROM milk_tea AS m; ---94.5
SELECT SUM(m.sale_price - m.in_price) FROM milk_tea AS m; ---31.5
SELECT SUM(IFNULL(m.sale_price, 0) - m.in_price) FROM milk_tea AS m; ---16
image.png
SELECT SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w = '100g'; ---34
SELECT SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w = '150g'; ---35
image.png
3.均值函数 AVG
SELECT AVG(m.sale_price) FROM milk_tea AS m; ---13.5
SELECT SUM(m.sale_price)/COUNT(m.sale_price) FROM milk_tea AS m; ---13.5
SELECT SUM(m.sale_price)/COUNT(1) FROM milk_tea AS m; ---11.8125
image.png
image.png
4.最大值函数 MAX，最小值函数 MIN
SELECT MAX(m.sale_price) FROM milk_tea AS m;
SELECT MIN(m.sale_price) FROM milk_tea AS m;
image.png
SELECT COUNT(m.sale_price), SUM(m.sale_price), AVG(m.sale_price), MIN(m.sale_price), MAX(m.sale_price) FROM milk_tea AS m;
image.png
image.png
二.分组过滤
1.GROUP BY
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m GROUP BY m.net_w;
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w IN ('100g', '150g') GROUP BY m.net_w;
SELECT m.net_w, COUNT(m.sale_price) FROM milk_tea AS m WHERE m.net_w IN('100g', '150g') GROUP BY m.net_w;
image.png
image.png
2.HAVING
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m GROUP BY m.net_w HAVING SUM(m.sale_price) > 20;
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w IN('100g', '150g') GROUP BY m.net_w;
image.png
SELECT p.prod_name, p.sale_price, p.class FROM prod_info AS p WHERE p.sale_price > 10 GROUP BY p.prod_name HAVING p.class = '零食';
image.png
image.png
SELECT * FROM prod_info AS p;
SELECT p.class, COUNT(1) FROM prod_info AS p GROUP BY p.class;
SELECT p.class, AVG(p.sale_price) FROM prod_info AS p GROUP BY p.class HAVING COUNT(1) > 4;
SELECT p.class, COUNT(1) FROM prod_info AS p WHERE p.class != '零食' GROUP BY p.class;
SELECT p.class, COUNT(1) FROM prod_info AS p WHERE p.sale_price > 10 GROUP BY p.class;
SELECT p.prod_name, p.sale_price FROM prod_info AS p WHERE p.sale_price < 10 AND p.class = '零食' GROUP BY p.prod_name;
SELECT p.prod_name, p.sale_price FROM prod_info AS p WHERE p.sale_price < 10 AND p.class IN('零食') GROUP BY p.prod_name;
SELECT p.prod_name, p.sale_price, p.class FROM prod_info AS p WHERE p.sale_price > 10 GROUP BY p.prod_name HAVING p.class = '零食';
image.png
三.今日代码
-- COUNT SUM AVG MAX MIN
SELECT COUNT(1) FROM milk_tea AS m;
SELECT COUNT(m.prod_name) FROM milk_tea AS m;
SELECT COUNT(m.pro_date) FROM milk_tea AS m;
SELECT COUNT(m.sale_price) FROM milk_tea AS m;
SELECT COUNT(DISTINCT m.sale_price), COUNT(DISTINCT m.pro_date) FROM milk_tea AS m;
SELECT DISTINCT m.sale_price FROM milk_tea AS m;
SELECT SUM(m.in_price) FROM milk_tea AS m; ---78.5
SELECT SUM(m.in_price * 1.1) FROM milk_tea AS m; ---86.35
SELECT SUM(m.sale_price) FROM milk_tea AS m; ---94.5
SELECT SUM(m.sale_price - m.in_price) FROM milk_tea AS m; ---31.5
SELECT SUM(IFNULL(m.sale_price, 0) - m.in_price) FROM milk_tea AS m; ---16
SELECT AVG(m.sale_price) FROM milk_tea AS m; ---13.5
SELECT SUM(m.sale_price)/COUNT(m.sale_price) FROM milk_tea AS m; ---13.5
SELECT SUM(m.sale_price)/COUNT(1) FROM milk_tea AS m; ---11.8125
SELECT SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w = '100g'; ---34
SELECT SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w = '150g'; ---35
SELECT MAX(m.sale_price) FROM milk_tea AS m;
SELECT MIN(m.sale_price) FROM milk_tea AS m;
SELECT COUNT(m.sale_price), SUM(m.sale_price), AVG(m.sale_price), MIN(m.sale_price), MAX(m.sale_price) FROM milk_tea AS m;
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m GROUP BY m.net_w;
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w IN ('100g', '150g') GROUP BY m.net_w;
SELECT m.net_w, COUNT(m.sale_price) FROM milk_tea AS m WHERE m.net_w IN('100g', '150g') GROUP BY m.net_w;
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m GROUP BY m.net_w HAVING SUM(m.sale_price) > 20;
SELECT m.net_w, SUM(m.sale_price) FROM milk_tea AS m WHERE m.net_w IN('100g', '150g') GROUP BY m.net_w;
SELECT * FROM prod_info AS p;
SELECT p.class, COUNT(1) FROM prod_info AS p GROUP BY p.class;
SELECT p.class, AVG(p.sale_price) FROM prod_info AS p GROUP BY p.class HAVING COUNT(1) > 4;
SELECT p.class, COUNT(1) FROM prod_info AS p WHERE p.class != '零食' GROUP BY p.class;
SELECT p.class, COUNT(1) FROM prod_info AS p WHERE p.sale_price > 10 GROUP BY p.class;
SELECT p.prod_name, p.sale_price FROM prod_info AS p WHERE p.sale_price < 10 AND p.class = '零食' GROUP BY p.prod_name;
SELECT p.prod_name, p.sale_price FROM prod_info AS p WHERE p.sale_price < 10 AND p.class IN('零食') GROUP BY p.prod_name;
SELECT p.prod_name, p.sale_price, p.class FROM prod_info AS p WHERE p.sale_price > 10 GROUP BY p.prod_name HAVING p.class = '零食';
四.课后作业
Q1：使用聚合函数完成如下操作。
1、产品信息表中一共有多少产品？
SELECT COUNT(1) FROM prod_info;
2、有哪些产品类别，每个类别分别又有多少种产品？
SELECT p.class, COUNT(p.class) FROM prod_info AS p GROUP BY p.class;
3、一共有多少客户购买了商品？
SELECT COUNT(DISTINCT o.cust_id) FROM order_list AS o;
4、哪些客户购买了商品，分别购买了多少？
SELECT o.cust_id,COUNT(o.cust_id) FROM order_list AS o GROUP BY o.cust_id;
Q2：使用 WHERE 和 HAVING 对数据记录进行正确过滤。
1、各类别中，产品销售价在 10 块以上的分别有多少？
SELECT p.class, COUNT(1) AS quantity FROM prod_info AS p WHERE p.sale_price > 10 GROUP BY p.class;
2、各类别中，产品数量在 5 件以上的分别有哪些？
SELECT p.class,COUNT(1) AS numbers FROM prod_info AS p GROUP BY p.class HAVING COUNT(1) > 5;
3、购买商品超过 5 件的用户有哪些？
SELECT o.cust_id,SUM(o.quantity) AS numbers FROM order_list AS o GROUP BY o.cust_id HAVING SUM(quantity) > 5;
Q3：写出我们所学过的所有子句，以及在完整语句中的书写顺序。并且指出各子句的操作
对象以及使用注意事项。
答：
SELECT...FROM...WHERE...GROUP BY... HAVING...ORDER BY...;
SELECT...FROM... 是必须子句，SELECT的操作对象是列名，FROM的操作对象是表名。
WHERE...子句用来过滤行，操作对象是针对列的关系表达式。
GROUP BY...子句用来进行分组，操作对象是聚合键，也是列名。要求SELECT部分有聚合键。
HAVING...子句用来对分组结果进行筛选，操作对象是聚合函数，使用前提是必须存在GROUP BY子句。
ORDER BY...子句对查询结果进行排序，它一定是查询语句的最后一条句子。