access数据库SQL语句更新查询 如果借阅时间超过一个月还未还书，将记录中”是否超期”改为true

你漏掉了set，先补上去看看

update 借书登记表 set 是否超期 = -1where 还书日期 - 借书日期 >30

-- 记录每一本图书借出和还回的 *** 作

-- 书的信息

DROP DATABASE IF EXISTS db_lib

CREATE DATABASE db_lib

use db_lib

SET @READER_MAX = 10

SET @EVERY_DAY_FEE=0.1

SELECT 10 INTO @temp

-- 新建相关的表

CREATE TABLE books (

id INT PRIMARY KEY AUTO_INCREMENT,

name CHAR(255) NOT NULL,

price DECIMAL(8,2) DEFAULT 0

)

CREATE TABLE readers (

id INT PRIMARY KEY AUTO_INCREMENT,

name CHAR(255) NOT NULL,

borrowed INT DEFAULT 0

)

CREATE TABLE lib_books (

id INT PRIMARY KEY AUTO_INCREMENT,

info INT,

FOREIGN KEY(info) REFERENCES books(id),

stat CHAR(10) NOT NULL DEFAULT "在馆"

)

-- 记录借书和还书

CREATE TABLE lib_loan (

id INT AUTO_INCREMENT,

who INT,

which INT,

check_out DATETIME NOT NULL DEFAULT NOW(),

check_in DATETIME DEFAULT NULL,

renew BOOLEAN NOT NULL DEFAULT 0,

latest DATE NOT NULL,

fee DECIMAL(8,2) DEFAULT NULL,

PRIMARY KEY(id),

FOREIGN KEY(who) REFERENCES readers(id),

FOREIGN KEY(which) REFERENCES lib_books(id)

)

-- 给馆藏图书添加10本书

-- 存储过程

DELIMITER $$$

CREATE PROCEDURE add_books( IN n INT)

BEGIN

-- 需要有多行数据放入变量，需要用 游标 cursor

-- i 局部变量

DECLARE i INT DEFAULT 1

-- @temp全局变量

SELECT COUNT(*) INTO @temp

FROM books

WHILE i<=n DO

INSERT INTO lib_books (info) VALUES ( FLOOR(RAND()*@temp)+1 )

SET i = i+1

END WHILE

END $$$

DELIMITER

-- 触发器 trigger ,管理图书被借出后，藏书和读者信息的维护

-- 表中数据相关的 *** 作： 增 删 改 （查）

-- 一个表中某条记录被修改：OLD 代表原有的那条记录 NEW代表新的那条记录

-- [BEFORE | AFTER] [INSERT | UPDATE | (DELETE) ]

DELIMITER $$$

CREATE TRIGGER before_insert_loan

BEFORE INSERT ON lib_loan

FOR EACH ROW

BEGIN

-- OLD NEW 已知

DECLARE v1 CHAR(100)

DECLARE v2 INT

SET NEW.latest =DATE_ADD(NEW.check_out,INTERVAL 1 month)

-- 只能修改NEW

SELECT stat INTO v1

FROM lib_books

WHERE id=NEW.which

SELECT borrowed INTO v2

FROM readers

WHERE id=NEW.who

IF ( v1<>"在馆" ) THEN

SIGNAL SQLSTATE '45000'

SET MESSAGE_TEXT = "图书已借出！"

END IF

IF (v2=@READER_MAX) THEN

SIGNAL SQLSTATE '45000'

SET MESSAGE_TEXT = "读者已经到达最大借阅数！"

END IF

END $$$

DELIMITER

-- 书借出的数据维护

DELIMITER $$$

CREATE TRIGGER after_insert_loan

AFTER INSERT ON lib_loan

FOR EACH ROW

BEGIN

UPDATE lib_books

SET stat = "已借出"

WHERE id = NEW.which

UPDATE readers

SET borrowed = borrowed + 1

WHERE id = NEW.who

END $$$

DELIMITER

-- 书归还的数据维护

DELIMITER $$$

CREATE TRIGGER after_update_loan

AFTER UPDATE ON lib_loan

FOR EACH ROW

BEGIN

IF(OLD.check_in is NULL AND NEW.check_in is NOT NULL) THEN

UPDATE lib_books

SET stat="在馆"

WHERE id= NEW.which

UPDATE readers

SET borrowed=borrowed -1

WHERE id=OLD.who

END IF

END $$$

DELIMITER

DELIMITER $$$

CREATE TRIGGER before_update_loan

BEFORE UPDATE ON lib_loan

FOR EACH ROW

BEGIN

DECLARE x INT

IF(OLD.renew=0 AND NEW.renew=1 ) THEN

SET NEW.latest=DATE_ADD(OLD.latest,INTERVAL 1 month)

END IF

-- 计算超期费用

IF(OLD.check_in is NULL AND NEW.check_in is NOT NULL) THEN

SET x=DATEDIFF(NEW.check_in,NEW.latest)

IF(x<=0 )THEN

SET NEW.fee =0

ELSE

SET NEW.fee=@EVERY_DAY_FEE*x

END IF

END IF

END $$$

DELIMITER

-- 添加若干的测试数据

INSERT INTO books (name, price)

VALUES

("javascript程序设计", 19.8),

("数据库系统开发", 20.8),

("mysql数据库必知必会", 28.8)

INSERT INTO readers ( name )

VALUES

("Alice"),

("Bob"),

("Carl")

-- 测试语句

SHOW TABLES

-- 根据书的信息添加10本馆藏图书

CALL add_books( 10)

SELECT * from lib_books

-- 借书

-- 2号读者借了2号书

INSERT INTO lib_loan (who , which ) VALUES (2,2)

INSERT INTO lib_loan (who , which ) VALUES (2,3)

INSERT INTO lib_loan (who , which ) VALUES (2,4)

INSERT INTO lib_loan (who , which ) VALUES (1,2)

INSERT INTO lib_loan (who , which ) VALUES (1,6)

INSERT INTO lib_loan (who , which ) VALUES (2,1)

INSERT INTO lib_loan (who , which ) VALUES (1,1)

-- 还书

UPDATE lib_loan

SET check_in='2022-12-15 12:00:00'

WHERE id = 1

-- 续借

UPDATE lib_loan

SET renew = 1

WHERE id = 4

SELECT * FROM lib_books

SELECT * FROM readers

SELECT * FROM lib_loan