Mysql 创建自定义函数

为什么要创建自定义函数

在使用mysql的过程中，mysql自带的函数可能不能完成我们的业务需求，这时就需要自定义函数,

函数的作用

函数包括数学函数、字符串函数、日期和时间函数、条件判断函数、系统信息函数、加密函数、格式化函数等。通过这些函数，可以简化用户的操作。

函数创建的语法

CREATE FUNCTION func_name ( [func_parameter] ) //括号是必须的，参数是可选的
RETURNS type
[ characteristic ...] routine_body

• CREATE FUNCTION 用来创建函数的关键字；
• func_name 表示函数的名称；
• func_parameters为函数的参数列表，参数列表的形式为：[IN|OUT|INOUT] param_name type

1. IN：表示输入参数；
2. OUT：表示输出参数；
3. INOUT：表示既可以输入也可以输出；
4. param_name：表示参数的名称；
5. type：表示参数的类型，该类型可以是MySQL数据库中的任意类型；

• RETURNS type：语句表示函数返回数据的类型；
• characteristic: 指定存储函数的特性，取值与存储过程时相同，详细请访问－MySQL存储过程使用;

示例

创建示例数据库、示例表与插入样例数据脚本：

create database hr;
use hr;
 
create table employees
(
    employee_id int(11) primary key not null auto_increment,
    employee_name varchar(50) not null,
    employee_sex varchar(10) default '男',
    hire_date datetime not null default current_timestamp,
    employee_mgr int(11),
    employee_salary float default 3000,
    department_id int(11)
);
 
 
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('David Tian','男',10,7500,1);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Black Xie','男',10,6600,1);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Moses Wang','男',10,4300,1);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Rena Ruan','女',10,5300,1);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Sunshine Ma','女',10,6500,2);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Scott Gao','男',10,9500,2);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Warren Si','男',10,7800,2);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Kaishen Yang','男',10,9500,3);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Simon Song','男',10,5500,3);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Brown Guan','男',10,5000,3);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Eleven Chen','女',10,3500,2);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Cherry Zhou','女',10,5500,4);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Klause He','男',10,4500,5);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Maven Ma','男',10,4500,6);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Stephani Wang','女',10,5500,7);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Jerry Guo','男',10,8500,1);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Gerardo Garza','男',10,25000,8);
insert into employees(employee_name,employee_sex,employee_mgr,employee_salary,department_id) values ('Derek Wu','男',10,5500,5);
 
 
select * from employees;

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创建函数－根据ID获取员工姓名与员工工资

DELIMITER //
CREATE FUNCTION GetEmployeeInformationByID(id INT)
RETURNS VARCHAR(300)
BEGIN
    RETURN(SELECT CONCAT('employee name:',employee_name,'---','salary: ',employee_salary) FROM employees WHERE employee_id=id);
END//
DELIMITER ;

调用函数

在MySQL——函数的使用方法与MySQL内部函数的使用方法一样。

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