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;

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