[Mysql] 更新数据

使用UPDATE语句可以对数据表中的现有数据进行更新

语法结构

UPDATE 表名
SET 列1=值1,列2=值2...
[WHERE 条件]
[ORDER BY...]
[LIMIT row_count];

SET命令用来将新值赋给被更新的列

ORDER BY: 按照指定的顺序对行进行更新

LIMIT: 限制可更新的行数

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基本的UPDATE语句主要由3部分组成，分别是：

1.要更新的表

2.列名和它们的新值

3.确定要更新行的过滤条件

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在更新多个列时，只需要使用单个SET命令，每个“列=值”对之间用逗号分隔(最后一列之后不用逗号)

如果WHERE条件没有匹配到任何记录，UPDATE语句不会报错，也不会有任何记录被更新

练习案例

导入数据

DROP TABLE IF EXISTS `prod_info`;
CREATE TABLE `prod_info`  (
  `prod_id` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `prod_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `brand` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `type` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `class` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `cost` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `sale_price` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `supplier_id` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `prod_info` VALUES ('10001', '抽纸', '洁柔', '120抽*8', '日用品', '20.11', '28.8', 'NJ0001');
INSERT INTO `prod_info` VALUES ('10002', '抽纸', '维达', '120抽*8', '日用品', '18.02', '25.5', 'NJ0002');
INSERT INTO `prod_info` VALUES ('10003', '抽纸', '洁云', '120抽*8', '日用品', '19.11', '26.8', 'SH0001');
INSERT INTO `prod_info` VALUES ('10004', '洗衣液', '蓝月亮', '2.5kg', '日用品', '33.43', '43.8', 'SH0002');
INSERT INTO `prod_info` VALUES ('10005', '洗衣液', '奥妙', '2.5kg', '日用品', '35.82', '49.9', 'SZ0001');

prod_info表

注意:下述案例1-4的表数据都是使用上述的prod_info表中的数据

案例1: 将prod_info表中class字段中的'日用品'更改为'生活日用品'

UPDATE prod_info SET class='生活日用品';

结果展示:

如果执行UPDATE而不带WHERE子句，则表中每个行都将用新值更新

案例2: 将prod_id为'10001'该行记录中的class字段的'生活日用品'更换为'抽纸类日用品'

UPDATE prod_info
SET class='抽纸类日用品'
WHERE prod_id='10001';

结果展示:

案例3: 对商品打九折(赋的新值可以是计算表达式)

在UPDATE语句中，更新字段时可以使用表达式

UPDATE prod_info
SET sale_price = sale_price * 0.9;

结果展示:

未对商品打九折

对商品打九折

案例4: 将prod_id为'10002'和'10003'该2行记录中的class字段值设置为空

为了删除某个列的值，可设置它为NULL(假如表定义允许NULL值)

原数据

UPDATE prod_info
SET class=NULL
WHERE prod_id='10002' OR prod_id='10003';

结果展示:

其中NULL用来去除class列中的值 

补充练习案例:将所有to_date为9999-01-01的全部更新为NULL

导入数据

drop table if exists titles_test;
CREATE TABLE  titles_test (
   id int(11) not null primary key,
   emp_no  int(11) NOT NULL,
   title  varchar(50) NOT NULL,
   from_date  date NOT NULL,
   to_date  date DEFAULT NULL);

insert into titles_test values
('1', '10001', 'Senior Engineer', '1986-06-26', '9999-01-01'),
('2', '10002', 'Staff', '1996-08-03', '9999-01-01'),
('3', '10003', 'Senior Engineer', '1995-12-03', '9999-01-01'),
('4', '10004', 'Senior Engineer', '1995-12-03', '9999-01-01'),
('5', '10001', 'Senior Engineer', '1986-06-26', '9999-01-01'),
('6', '10002', 'Staff', '1996-08-03', '9999-01-01'),
('7', '10003', 'Senior Engineer', '1995-12-03', '9999-01-01');

titles_test表

问题:将所有to_date为9999-01-01的全部更新为NULL,且 from_date更新为2001-01-01

UPDATE titles_test SET to_date = NULL, from_date = '2001-01-01'
WHERE to_date = '9999-01-01';

结果展示:

案例5

UPDATE语句中可以使用子查询，使得能用SELECT语句检索出的数据更新列数据

导入数据

DROP TABLE IF EXISTS `Customers`;
CREATE TABLE `Customers` (
  `id` int(11) NOT NULL,
  `customer` varchar(255) DEFAULT NULL,
  `tutor` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

INSERT INTO `Customers` VALUES ('1', 'Odin', null);
INSERT INTO `Customers` VALUES ('2', 'Jack', 'Rita');
INSERT INTO `Customers` VALUES ('3', 'Harry', null);
INSERT INTO `Customers` VALUES ('4', 'Sun', 'Ted');
INSERT INTO `Customers` VALUES ('5', 'Summer', null);

DROP TABLE IF EXISTS `Tutors`;
CREATE TABLE `Tutors` (
  `id` int(11) NOT NULL,
  `tutor` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

INSERT INTO `Tutors` VALUES ('1', 'tutor1');
INSERT INTO `Tutors` VALUES ('2', 'tutor2');
INSERT INTO `Tutors` VALUES ('3', 'tutor3');
INSERT INTO `Tutors` VALUES ('4', 'tutor4');

Customers表(客户信息表)

customer: 客户名   tutor:助教名 

在Customers表中，有些客户没有助教(tutor字段取值为Null)

Tutors表(助教信息表)

问题:从Tutors表中随机选取一名助教，为那些没有助教的客户提供帮助

UPDATE Customers
SET tutor = (SELECT tutor
             FROM Tutors
             ORDER BY RAND()
             LIMIT 1)
WHERE tutor IS NULL;

结果展示:Customer表

UPDATE JOIN语句 跨表更新

UPDATE 表1 
JOIN 表2 
ON 表1.列名 = 表2.列名
SET 列名 = 表达式 [, 列名 = 表达式 ...]
[WHERE 条件];

说明:
1.利用表2中的数据更新表1，要求两个表必须存在关联字段
2.表1和表2关联的条件为表1.列名 = 表2.列名

案例1

导入数据

DROP TABLE IF EXISTS `emp`;
CREATE TABLE `emp`  (
  `emp_id` int(11) NOT NULL,
  `emp_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `gender` enum('男','女') CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT '男',
  `salary` float(255, 2) DEFAULT NULL,
  `phone` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `dept_id` int(255) NOT NULL,
  `dept_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  PRIMARY KEY (`emp_id`, `dept_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `emp` VALUES (1, 'Jack', '男', 4725.00, '15937321555', 11, NULL);
INSERT INTO `emp` VALUES (1101, 'Mark', '男', 7455.00, '15903732155', 11, NULL);
INSERT INTO `emp` VALUES (1102, 'Rose', '女', 6510.00, '15937321666', 12, NULL);
INSERT INTO `emp` VALUES (1103, 'Jerry', '男', 3885.00, '15537312999', 12, NULL);


DROP TABLE IF EXISTS `dept`;
CREATE TABLE `dept`  (
  `dept_id` int(11) NOT NULL,
  `dept_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  PRIMARY KEY (`dept_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `dept` VALUES (11, '人事部');
INSERT INTO `dept` VALUES (12, '财务部');

emp表

dept表

UPDATE emp 
JOIN dept 
ON emp.dept_id = dept.dept_id
SET emp.dept_name = dept.dept_name
WHERE emp.dept_id = 11;

结果展示: emp表

案例2

有两个表 stu和 certificate，使用stu表的s_name 和phone列的数据更新certificate 表

导入数据

DROP TABLE IF EXISTS `stu`;
CREATE TABLE `stu`  (
  `s_no` int(11) NOT NULL,
  `s_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `birth` timestamp(0) DEFAULT NULL,
  `phone` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `addr` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  PRIMARY KEY (`s_no`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `stu` VALUES (1, 'Jack', '1999-01-23 00:00:00', '13703735566', 'Beijing');
INSERT INTO `stu` VALUES (2, 'Mark', '1999-10-03 00:00:00', '13783735566', 'Beijing');
INSERT INTO `stu` VALUES (3, 'Rose', '2000-11-21 00:00:00', '13783735522', 'Shanghai');
INSERT INTO `stu` VALUES (4, 'John', '2000-03-04 00:00:00', '18503735214', 'Guangzhou');
INSERT INTO `stu` VALUES (5, 'Jerry', '2001-04-25 00:00:00', '13303735266', 'Guangzhou');


DROP TABLE IF EXISTS `certificate`;
CREATE TABLE `certificate`  (
  `s_no` int(11) NOT NULL,
  `s_name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `phone` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `certificate` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  PRIMARY KEY (`s_no`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `certificate` VALUES (1, NULL, NULL, '英语四级');
INSERT INTO `certificate` VALUES (2, NULL, NULL, '英语四级');
INSERT INTO `certificate` VALUES (3, NULL, NULL, '英语六级');
INSERT INTO `certificate` VALUES (4, NULL, NULL, '计算机二级');
INSERT INTO `certificate` VALUES (5, NULL, NULL, '英语四级');

stu表

certificate表

UPDATE certificate AS c
JOIN stu AS s
ON c.s_no = s.s_no
SET c.s_name = s.s_name, c.phone = s.phone;

结果展示: certificate表

更新的指导原则

1.如果执行UPDATE而不带WHERE子句，则表中每个行都将用新值更新,除非确实打算更新每一行，否则绝对不要使用不带WHERE子句的UPDATE语句

2.在执行UPDATE语句时要非常小心，最好先用SELECT语句来测试WHERE条件是否筛选出了期望的记录集，然后再用UPDATE更新 (MySQL没有撤销(undo)按钮,应该非常小心地使用UPDATE，否则你会发现自己更新了错误的数据)