怎樣在mysql中建立函數

在mysql中可以通過語法「CREATE FUNCTION func_name ( [func_parameter] )」來建立函數，其中「CREATE FUNCTION」是用來建立函數的關鍵字。

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在MySQL資料庫中建立函數(Function)

語法

CREATE FUNCTION func_name ( [func_parameter] ) //括號是必須的，引數是可選的
RETURNS type
[ characteristic ...] routine_body

CREATE FUNCTION 用來建立函數的關鍵字；

func_name 表示函數的名稱；

func_parameters為函數的參數列，參數列的形式為：[IN|OUT|INOUT] param_name type

IN：表示輸入引數；

OUT：表示輸出引數；

INOUT：表示既可以輸入也可以輸出；

param_name：表示引數的名稱；

type：表示引數的型別，該型別可以是MySQL資料庫中的任意型別；

RETURNS type：語句表示函數返回資料的型別；

characteristic: 指定儲存函數的特性，取值與儲存過程時相同，詳細請存取－MySQL儲存過程使用;

範例

建立範例資料庫、範例表與插入樣例資料指令碼：

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;

建立函數－根據ID獲取員工姓名與員工工資

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 ;

呼叫函數

在MySQL——函數的使用方法與MySQL內部函數的使用方法一樣。

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