本文实例讲述了MySQL使用集合函数进行查询操作。，具体如下：
COUNT函数
| SELECT COUNT(*) AS cust_num from customers;SELECT COUNT(c_email) AS email_num FROM customers;SELECT o_num, COUNT(f_id) FROM orderitems GROUP BY o_num; |
SUM函数
| SELECT SUM(quantity) AS items_total FROM orderitems WHERE o_num = 30005;SELECT o_num, SUM(quantity) AS items_total FROM orderitems GROUP BY o_num; |
AVG函数
| SELECT AVG(f_price) AS avg_price FROM fruits WHERE s_id = 103;SELECT AVG(f_price) AS avg_price FROM fruits group by s_id; |
MAX函数
| SELECT MAX(f_price) AS max_price FROM fruits;SELECT s_id, MAX(f_price) AS max_price FROM fruits GROUP BY s_id;SELECT MAX(f_name) from fruits; |
MIN函数
| SELECT MIN(f_price) AS min_price FROM fruits;SELECT s_id, MIN(f_price) AS min_price FROM fruits GROUP BY s_id; |
【例.34】查询customers表中总的行数
| SELECT COUNT(*) AS cust_num from customers; |
【例.35】查询customers表中有电子邮箱的顾客的总数，输入如下语句：
| SELECT COUNT(c_email) AS email_numFROM customers; |
【例.36】在orderitems表中，使用COUNT()函数统计不同订单号中订购的水果种类
| SELECT o_num, COUNT(f_id) FROM orderitems GROUP BY o_num; |
【例.37】在orderitems表中查询30005号订单一共购买的水果总量，输入如下语句：
| SELECT SUM(quantity) AS items_totalFROM orderitemsWHERE o_num = 30005; |
【例.38】在orderitems表中，使用SUM()函数统计不同订单号中订购的水果总量
| SELECT o_num, SUM(quantity) AS items_totalFROM orderitemsGROUP BY o_num; |
【例.39】在fruits表中，查询s_id=103的供应商的水果价格的平均值，SQL语句如下：
| SELECT AVG(f_price) AS avg_priceFROM fruitsWHERE s_id = 103; |
【例.40】在fruits表中，查询每一个供应商的水果价格的平均值，SQL语句如下：
| SELECT s_id,AVG(f_price) AS avg_priceFROM fruitsGROUP BY s_id; |
【例.41】在fruits表中查找市场上价格最高的水果，SQL语句如下：
| mysql>SELECT MAX(f_price) AS max_price FROM fruits; |
【例7.42】在fruits表中查找不同供应商提供的价格最高的水果
| SELECT s_id, MAX(f_price) AS max_priceFROM fruitsGROUP BY s_id; |
【例.43】在fruits表中查找f_name的最大值，SQL语句如下
| SELECT MAX(f_name) from fruits; |
