MariaDB中的sum()函数用来做啥 用法是怎样

这篇文章主要讲解了“MariaDB中的sum()函数用来做什么，用法是怎样”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“MariaDB中的sum()函数用来做什么，用法是怎样”吧！

MariaDB SUM()函数用于返回表达式求和的值。

语法：

SELECT SUM(aggregate_expression)

FROM tables

[WHERE conditions];

数据准备

在"testdb"数据库中创建一个"students"表，并插入一些数据。参考以下创建语句 -

USE testdb;

DROP TABLE students;

-- 创建新表

CREATE TABLE students(

student_id INT NOT NULL AUTO_INCREMENT,

student_name VARCHAR(100) NOT NULL,

student_address VARCHAR(40) default NULL,

admission_date DATE,

score float(4, 1) default NULL,

PRIMARY KEY ( student_id )

);

-- 插入数据

INSERT INTO students

(student_id, student_name, student_address,score, admission_date)

VALUES(1,'Maxsu','Haikou', 99.5,'2017-01-07 00:00:00');

INSERT INTO students

(student_id, student_name, student_address, score, admission_date)

VALUES

(2,'Crurry','Beijing',86,'2016-05-07 00:00:00'),

(3,'JMaster','Beijing',91,'2016-05-07 00:00:00'),

(4,'Mahesh','Guangzhou',78,'2016-06-07 00:00:00'),

(5,'Kobe','Shanghai',89,'2016-02-07 00:00:00'),

(6,'Blaba','Shengzhen',100,'2016-08-07 00:00:00');

1. SUM()函数与单表达式

示例：

计算student_id大于1的Student表的总分数。参考以下查询语句 -

SELECT SUM(Score) AS "Total Score"

FROM students

WHERE student_id > 1;

执行上面查询语句，得到以下结果 -

MariaDB [testdb]> SELECT SUM(Score) AS "Total Score"

-> FROM students

-> WHERE student_id > 1;

+-------------+

| Total Score |

+-------------+

| 444.0 |

+-------------+

1 row in set (0.00 sec)

2. SUM()函数与DISTINCT子句

可以使用SUM函数的DISTINCT子句来避免重复值的总和。

再插入一条重复的数据 -

INSERT INTO students

(student_name, student_address,score, admission_date)

VALUES('Maxsu','Haikou', 99.5,'2017-11-07 00:00:00');

当前数据库中的记录如下 -

MariaDB [testdb]> select * from students;

+------------+--------------+-----------------+----------------+-------+

| student_id | student_name | student_address | admission_date | score |

+------------+--------------+-----------------+----------------+-------+

| 1 | Maxsu | Haikou | 2017-01-07 | 99.5 |

| 2 | Crurry | Beijing | 2016-05-07 | 86.0 |

| 3 | JMaster | Beijing | 2016-05-07 | 91.0 |

| 4 | Mahesh | Guangzhou | 2016-06-07 | 78.0 |

| 5 | Kobe | Shanghai | 2016-02-07 | 89.0 |

| 6 | Blaba | Shengzhen | 2016-08-07 | 100.0 |

| 7 | Maxsu | Haikou | 2017-11-07 | 99.5 |

+------------+--------------+-----------------+----------------+-------+

7 rows in set (0.00 sec)

示例：

SELECT SUM(DISTINCT Score) AS "Total Score"

FROM students

WHERE student_name = 'Maxsu';

执行上面查询语句，得到以下结果 -

MariaDB [testdb]> SELECT SUM(DISTINCT Score) AS "Total Score"

-> FROM students

-> WHERE student_name = 'Maxsu';

+-------------+

| Total Score |

+-------------+

| 99.5 |

+-------------+

1 row in set (0.00 sec)

到此这篇关于“MariaDB中的sum()函数用来做什么，用法是怎样”的文章就介绍到这了,更多相关内容请搜索群英网络以前的文章或继续浏览下面的相关文章，希望大家以后多多支持！

（编辑：银川站长网）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!