MySQL使用集合函数进行查询操作实例详解

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;

更多关于mysql相关内容感兴趣的读者可查看本站专题：《mysql常用函数大汇总》、《mysql日志操作技巧大全》、《mysql事务操作技巧汇总》、《mysql存储过程技巧大全》及《mysql数据库锁相关技巧汇总》

希望本文所述对大家mysql数据库计有所帮助。