insert into busi_table values("1001","gx", "11"); //failed,提示: ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`smb_man`.`busi_table`, CONSTRAINT `busi_table_ibfk_1` FOREIGN KEY (`repo_id`) REFERENCES `repo_table` (`repo_id`)) 3)增...
IDvarchar(15) COMMENT'身份证号',CONSTRAINTuq_Person_IDUNIQUE(email,ID),CONSTRAINTpk_PersonID_NamePRIMARYkey(P_id,P_Name) );descPersons; 创建unique约束成功 4.外键约束(转自:http://c.biancheng.net/view/2441.html) MySQL外键约束(FOREIGN KEY)是表的一个特殊字段,经常与主键约束一起使用。对于两个...
insert into busi_table values("1001","gx", "11"); //failed,提示: ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`smb_man`.`busi_table`, CONSTRAINT `busi_table_ibfk_1` FOREIGN KEY (`repo_id`) REFERENCES `repo_table` (`repo_id`)) 3)增...
alter table 表名 add constraint 约束名 foreign key(列名) references 其他表(其他表的列名) [on update 等级] [on delete 等级]; 例如:alter table uniquetest add constraint fc foreign key(name) references testtab(fname) on delete cascade on update cascade; 如何查看某个表的外键约束名: select * ...
约束(Constraints) MySQL的约束是一种规则,用于限制表中的数据以确保数据的准确性和可靠性。约束可以在创建表时定义,也可以在表创建后添加。以下是MySQL中常用的几种约束: 1、NOT NULL 约束 代码语言:javascript 代码运行次数:0 运行 AI代码解释 sql`CREATE TABLE students ( ...
The MySQL implementation of foreign key constraints differs from the SQL standard in the following key respects: If there are several rows in the parent table with the same referenced key value, InnoDB performs a foreign key check as if the other parent rows with the same key value do not ...
一种限制,用于限制表中的数据,为了保证表中的数据的准确和可靠性。MySQL数据库通过约束(constraints)防止无效的数据进入到表中,以保护数据的实体完整性。 约束的分类 在MySQL中,主要有六种约束: 1、NOT NULL:非空约束,用于约束该字段的值不能为空。比如姓名、学号等。
SET DEFAULTis also supported by the MySQL Server but is currently rejected as invalid byInnoDB. Since MySQL does not support deferred constraint checking,NO ACTIONis treated asRESTRICT. For the exact syntax supported by MySQL for foreign keys, seeSection 15.1.20.5, “FOREIGN KEY Constraints”. ...
Mysql FOREIGN KEY Constraints InnoDB支持 foreign key constraints. constraint definition inInnoDBlooks like this: [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name, ...) REFERENCEStbl_name(index_col_name,...) [ON DELETEreference_option]...
SELECT * FROM information_schema.`TABLE_CONSTRAINTS` WHERE table_name='表名' 删除的方法: ALTER TABLE student4 DROP INDEX 索引名 PRIMARY KEY约束 主键约束相当于唯一约束+非空约束。主键约束的列不允许重复,也不允许出现空值 一个表最多有一个主键约束,建立主键约束可以在列级别创建,也可以在表级别创建...