SQL HAVING 子句

SQL 中的 HAVING 子句用于筛选分组 ( GROUP BY ) 后的各组数据,相当于 SELECT 语句中的 WHERE 语句

SELECT column_name, aggregate_function(column_name) FROM table_name WHERE column_name operator value GROUP BY column_name HAVING aggregate_function(column_name) operator value;

HAVING 子句一般跟在 GROUP BY 子句后面

演示数据

先在 MySQL 数据库运行下面的语句创建测试数据

CREATE DATABASE IF NOT EXISTS twle default character set utf8mb4 collate utf8mb4_unicode_ci;

USE twle;

DROP TABLE IF EXISTS `lession_views`;

CREATE TABLE `lession_views` (
    uniq bigint(20) primary key NOT NULL default '0' ,
    lession_name varchar(32) NOT NULL default '',
    lession_id int(11) NOT NULL default '0',
    date_at  int(11) NOT NULL default '0',
    views int(11) NOT NULL default '0'
);

INSERT INTO lession_views(uniq,lession_name,lession_id,date_at,views) VALUES
(20170511000001,'Python 基础教程',1,20170511,320),
(20170511000002,'Scala 基础教程', 2,20170511,22),
(20170511000003,'Ruby 基础教程', 3, 20170511,49),
(20170512000001,'Python 基础教程',1,20170512,220),
(20170512000002,'Scala 基础教程',2,20170512,12),
(20170512000003,'Ruby 基础教程',3,20170512,63),
(20170513000001,'Python 基础教程',1,20170513,441),
(20170513000002,'Scala 基础教程',2,20170513,39),
(20170513000003,'Ruby 基础教程',3,20170513,87);

使用 SELECT * FROM lession_views; 运行结果如下

+----------------+---------------------+------------+----------+-------+
| uniq           | lession_name        | lession_id | date_at  | views |
+----------------+---------------------+------------+----------+-------+
| 20170511000001 | Python 基础教程     |          1 | 20170511 |   320 |
| 20170511000002 | Scala 基础教程      |          2 | 20170511 |    22 |
| 20170511000003 | Ruby 基础教程       |          3 | 20170511 |    49 |
| 20170512000001 | Python 基础教程     |          1 | 20170512 |   220 |
| 20170512000002 | Scala 基础教程      |          2 | 20170512 |    12 |
| 20170512000003 | Ruby 基础教程       |          3 | 20170512 |    63 |
| 20170513000001 | Python 基础教程     |          1 | 20170513 |   441 |
| 20170513000002 | Scala 基础教程      |          2 | 20170513 |    39 |
| 20170513000003 | Ruby 基础教程       |          3 | 20170513 |    87 |
+----------------+---------------------+------------+----------+-------+

SQL HAVING 范例

我们先使用 GROUP BY 语句统计下所有课程的访问量

SELECT lession_name, SUM(views) FROM lession_views GROUP BY lession_name;

输出结果如下

mysql> SELECT lession_name, SUM(views) FROM lession_views GROUP BY lession_name; 
+---------------------+------------+
| lession_name        | SUM(views) |
+---------------------+------------+
| Python 基础教程     |        981 |
| Ruby 基础教程       |        199 |
| Scala 基础教程      |         73 |
+---------------------+------------+

如果我们需要选择总访问量在 100 以内的课程,那么可以使用下面的 SQL 语句

SELECT lession_name, SUM(views) as total_views FROM lession_views GROUP BY lession_name HAVING total_views < 100;

运行结果输出如下

mysql> SELECT lession_name, SUM(views) as total_views FROM lession_views GROUP BY lession_name HAVING total_views < 100;
+--------------------+-------------+
| lession_name       | total_views |
+--------------------+-------------+
| Scala 基础教程     |          73 |
+--------------------+-------------+

SQL 基础教程

关于   |   FAQ   |   我们的愿景   |   广告投放   |  博客

  简单教程,简单编程 - IT 入门首选站

Copyright © 2013-2018 简单教程 twle.cn All Rights Reserved.