本文实例讲述了MySQL使用集合函数进行查询操作。分享给大家供大家参考，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_num FROM 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_total FROM orderitems WHERE 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_total FROM orderitems GROUP 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_price FROM fruits WHERE 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_price FROM fruits GROUP 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_price FROM fruits GROUP 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;
【例.44】在fruits表中查找市场上价格最低的水果，SQL语句如下：
mysql>SELECT MIN(f_price) AS min_price FROM fruits;
【例.45】在fruits表中查找不同供应商提供的价格最低的水果
SELECT s_id, MIN(f_price) AS min_price FROM fruits GROUP BY s_id;
希望本文所述对大家MySQL数据库计有所帮助。
