MySQL存储过程

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#mysql #存储

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本文详细介绍SQL存储过程的基础概念，包括变量、参数、条件判断、循环、异常处理等，并通过具体实例展示如何创建和使用存储过程及函数，还涉及触发器的应用。

DELIMITER $$     
DROP PROCEDURE IF EXISTS HelloWorld$$   
CREATE PROCEDURE HelloWorld()   
BEGIN   
     SELECT "Hello World!";   
END$$   
DELIMITER ;    

 
　　3，变量

　　DECLARE声明，SET赋值

可以在DECLARE变量时用DEFAULT设置默认值，不设则为NULL
 
DECLARE counter INT DEFAULT 0;   
SET counter = counter+1;   

 
 　 4，参数

IN为默认类型，值必须在调用时指定，值不能返回（值传递）

OUT值可以返回（指针传递）

INOUT值必须在调用时指定，值可以返回

 
CREATE PROCEDURE test(a INT, OUT b FLOAT, INOUT c INT)   
CREATE PROCEDURE test(a INT, OUT b FLOAT, INOUT c INT)


 　  5，条件判断

--IF THEN、ELSEIF、ELSE、END IF
DELIMITER $$   
DROP PROCEDURE IF EXISTS discounted_price$$   
CREATE PROCEDURE discunted_price(normal_price NUMERIC(8, 2), OUT discount_price NUMERIC(8, 2))   
BEGIN   
     IF (normal_price > 500) THEN   
         SET discount_price = normal_price * .8;   
     ELSEIF (normal_price > 100) THEN   
         SET discount_price = normal_price * .9;   
     ELSE   
         SET discount_price = normal_price;   
     END IF;   
END$$     
DELIMITER ;   

6，循环

--LOOP、END LOOP 

 
DELIMITER $$    
DROP PROCEDURE IF EXISTS simple_loop$$    
CREATE PROCEDURE simple_loop(OUT counter INT)   
BEGIN   
     SET counter = 0;   
     my_simple_loop: LOOP   
         SET counter = counter+1;   
         IF counter = 10 THEN   
             LEAVE my_simple_loop;   
         END IF;   
     END LOOP my_simple_loop;   
END$$     
DELIMITER ;   

 

--WHILE DO、END WHILE

 
DELIMITER $$     
DROP PROCEDURE IF EXISTS simple_while$$   
CREATE PROCEDURE simple_while(OUT counter INT)   
BEGIN   
     SET counter = 0;   
     WHILE counter != 10 DO   
         SET counter = counter+1;   
     END WHILE;   
END$$     
DELIMITER ;   

 

--REPEAT、UNTILL

 
DELIMITER $$     
DROP PROCEDURE IF EXISTS simple_repeat$$     
CREATE PROCEDURE simple_repeat(OUT counter INT)   
BEGIN   
     SET counter = 0;   
     REPEAT   
         SET counter = counter+1;   
     UNTIL counter = 10 END REPEAT;   
END$$     
DELIMITER ;

7，异常处理

如果用cursor获取SELECT语句返回的所有结果集时应该定义NOT FOUND error handler来防止存储程序提前终结

如果SQL语句可能返回constraint violation等错误时应该创建一个handler来防止程序终结

8，数据库交互

INTO用于存储单行记录的查询结果

DECLARE total_sales NUMERIC(8, 2);   
SELECT SUM(sale_value) INTO total_sales FROM sales WHERE customer_id=in_customer_id;

　　CURSOR用于处理多行记录的查询结果

DELIMITER $$  
  
DROP PROCEDURE IF EXITS cursor_example$$  
CREATE PROCEDURE cursor_example()  
     READS SQL DATA  
BEGIN  
     DECLARE l_employee_id INT;  
     DECLARE l_salary NUMERIC(8,2);  
     DECLARE l_department_id INT;  
     DECLARE done INT DEFAULT 0;  
     DECLARE cur1 CURSOR FOR SELECT employee_id, salary, department_id FROM employees;  
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;  
  
     OPEN cur1;  
     emp_loop: LOOP  
         FETCH cur1 INTO l_employee_id, l_salary, l_department_id;  
         IF done=1 THEN  
             LEAVE emp_loop;  
         END IF;  
     END LOOP emp_loop;  
     CLOSE cur1;  
END$$  
DELIMITER ;

unbounded SELECT语句用于存储过程返回结果集

DELIMITER $$  

DROP PROCEDURE IF EXISTS sp_emps_in_dept$$  
CREATE PROCEDURE sp_emps_in_dept(in_employee_id INT)  
BEGIN  
     SELECT employee_id, surname, firstname, address1, address2, zipcode, date_of_birth FROM employees WHERE department_id=in_employee_id;  
END$$  
  
DELIMITER ;

UPDATE、INSERT、DELETE、CREATE TABLE等非查询语句也可以嵌入存储过程里

DELIMITER $$   
   
DROP PROCEDURE IF EXITS sp_update_salary$$   
CREATE PROCEDURE sp_update_salary(in_employee_id INT, in_new_salary NUMERIC(8,2))   
BEGIN   
     IF in_new_salary < 5000 OR in_new_salary > 500000 THEN   
         SELECT "Illegal salary: salary must be between $5000 and $500, 000";   
     ELSE   
         UPDATE employees SET salary=in_new_salary WHERE employee_id=in_employee_id;   
     END IF;  
END$$   
   
DELIMITER ;

　　9，使用CALL调用存储程序

DELIMITER $$   
   
DROP PROCEDURE IF EXISTS call_example$$   
CREATE PROCEDURE call_example(employee_id INT, employee_type VARCHAR(20))   
     NO SQL   
BEGIN   
     DECLARE l_bonus_amount NUMERIC(8,2);   
   
     IF employee_type='MANAGER' THEN   
         CALL calc_manager_bonus(employee_id, l_bonus_amount);   
     ELSE   
         CALL calc_minion_bonus(employee_id, l_bonus_amount);   
     END IF;   
     CALL grant_bonus(employee_id, l_bonus_amount);   
END$$   

DELIMITER ;

　　10，一个复杂的例子

CREATE PROCEDURE putting_it_all_together(in_department_id INT)   
     MODIFIES SQL DATA   
BEGIN   
     DECLARE l_employee_id INT;   
     DECLARE l_salary NUMERIC(8,2);   
     DECLARE l_department_id INT;   
     DECLARE l_new_salary NUMERIC(8,2);   
     DECLARE done INT DEFAULT 0;   
   
     DECLARE cur1 CURSOR FOR   
         SELECT employee_id, salary, department_id   
         FROM employees   
         WHERE department_id=in_department_id;   
   
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;   
   
     CREATE TEMPORARY TABLE IF NOT EXISTS emp_raises   
         (employee_id INT, department_id INT, new_salary NUMERIC(8,2));   
   
     OPEN cur1;   
     emp_loop: LOOP   
         FETCH cur1 INTO l_employee_id, l_salary, l_department_id;   
         IF done=1 THEN    /* No more rows */   
             LEAVE emp_loop;   
         END IF;   
         CALL new_salary(1_employee_id, l_new_salary); /* Get new salary */   
         IF (l_new_salary <> l_salary) THEN  /* Salary changed */   
             UPDATE employees   
                 SET salary=l_new_salary   
             WHERE employee_id=l_employee_id;   
            /* Keep track of changed salaries */   
             INSERT INTO emp_raises(employee_id, department_id, new_salary)   
                 VALUES (l_employee_id, l_department_id, l_new_salary);   
         END IF:   
     END LOOP emp_loop;   
     CLOSE cur1;   
    /* Print out the changed salaries */   
     SELECT employee_id, department_id, new_salary from emp_raises   
         ORDER BY employee_id;   
END;

　 11，存储方法

存储方法与存储过程的区别

1，存储方法的参数列表只允许IN类型的参数，而且没必要也不允许指定IN关键字

2，存储方法返回一个单一的值，值的类型在存储方法的头部定义

3，存储方法可以在SQL语句内部调用

4，存储方法不能返回结果集

语法：

CREATE   
     [DEFINER = { user | CURRENT_USER }]   
     PROCEDURE sp_name ([proc_parameter[,...]])   
     [characteristic ...] routine_body   
   
CREATE   
     [DEFINER = { user | CURRENT_USER }]   
     FUNCTION sp_name ([func_parameter[,...]])   
     RETURNS type   
     [characteristic ...] routine_body   
       
proc_parameter:   
     [ IN | OUT | INOUT ] param_name type   
       
func_parameter:   
     param_name type   
   
type:   
     Any valid MySQL data type   
   
characteristic:   
     LANGUAGE SQL   
   | [NOT] DETERMINISTIC   
   | { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }   
   | SQL SECURITY { DEFINER | INVOKER }   
   | COMMENT 'string'   
   
routine_body:   
     Valid SQL procedure statement

　各参数说明见CREATE PROCEDURE and CREATE FUNCTION Syntax

例子：

DELIMITER $$   
   
DROP FUNCTION IF EXISTS f_discount_price$$   
CREATE FUNCTION f_discount_price   
     (normal_price NUMERIC(8,2))   
     RETURNS NUMERIC(8,2)   
     DETERMINISTIC   
BEGIN   
     DECLARE discount_price NUMERIC(8,2);   
   
     IF (normal_price > 500) THEN   
         SET discount_price = normal_price * .8;   
     ELSEIF (normal_price >100) THEN   
         SET discount_price = normal_price * .9;   
     ELSE   
         SET discount_price = normal_price;   
     END IF;   
   
     RETURN(discount_price);   
END$$   
   
DELIMITER ;

　 12，触发器

触发器在INSERT、UPDATE或DELETE等DML语句修改数据库表时触发

触发器的典型应用场景是重要的业务逻辑、提高性能、监控表的修改等

触发器可以在DML语句执行前或后触发

DELIMITER $$   
   
DROP TRIGGER sales_trigger$$   
CREATE TRIGGER sales_trigger   
     BEFORE INSERT ON sales   
     FOR EACH ROW   
BEGIN   
     IF NEW.sale_value > 500 THEN   
         SET NEW.free_shipping = 'Y';   
     ELSE   
         SET NEW.free_shipping = 'N';   
     END IF;   
   
     IF NEW.sale_value > 1000 THEN   
         SET NEW.discount = NEW.sale_value * .15;   
     ELSE   
         SET NEW.discount = 0;   
     END IF;   
END$$   
   
DELIMITER ;