MySQL之存储函数详细介绍

CREATE FUNCTION 函数名(参数名 参数类型,...) 
RETURNS 返回值类型
BEGIN
	函数体   #函数体中肯定有 RETURN 语句
END

SELECT 函数名(实参列表)

DROP FUNCTION [IF EXISTS] 存储函数名

SHOW CREATE FUNCTION 存储函数名

SHOW FUNCTION STATUS [LIKE 'pattern']

#查询名称以select开头的存储函数
mysql> SHOW FUNCTION STATUS LIKE 'SELECT%';
*************************** 1. row ***************************
                  Db: test_db
                Name: SelectAllData
                Type: FUNCTION 
             Definer: root@localhost
            Modified: 2021-10-16 15:55:07
             Created: 2021-10-16 15:55:07
       Security_type: DEFINER
             Comment: 
character_set_client: utf8mb4
collation_connection: utf8mb4_general_ci
  Database Collation: utf8mb4_general_ci

SELECT * FROM information_schema.Routines
WHERE ROUTINE_NAME='存储函数名' [AND ROUTINE_TYPE = 'FUNCTION '];

ALTER FUNCTION 存储函数名;

#前提准备
CREATE TABLE employees
AS
SELECT * FROM atguigudb.`employees`; 

CREATE TABLE 
departments AS
SELECT * FROM atguigudb.`departments`; 

#1. 创建函数get_count(),返回公司的员工个数 #有参有返回 
SET GLOBAL log_bin_trust_function_creators = 1;

DELIMITER $
CREATE FUNCTION get_count()
RETURNS INT
BEGIN
	RETURN (SELECT COUNT(*) FROM employees);
END $
DELIMITER ;

#2. 创建函数ename_salary(),根据员工id，返回它的工资 
#查询表结构来看要返回数据的类型
DESC employees;

DELIMITER $
CREATE FUNCTION ename_salary(id INT)
RETURNS DOUBLE(8,2)
BEGIN
	RETURN (SELECT salary FROM employees WHERE employee_id = id);
END $
DELIMITER ;

#查询结果
SELECT ename_salary(100);