MySQL 创建函数(Function)

目标

如何在MySQL数据库中创建函数(Function)

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;

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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