Alter table borrow add constraint bks foreign key(Borrowbookid) rederences books(bookid) 通过select*from information_schema.KEY_COLUMN_USAGE;这条命令查询数据库中所有表的外键和主键 3.删除外键约束 语法格式:alter table 从表名 drop foreign key 外键名; 例:删除books6表Borrowbookid字段的外键约束,外键...
create table 表名(字段1 类型 PRIMARY KEY, 字段2 类型, 字段3 类型, 字段4 类型, FOREIGN KEY(字段3) REFERENCES class(id));这里定义字段3为外键,参照class表中的id主键字段 create table student2(id int PRIMARY KEY, name varchar(32), class_id int, sex enum('男', '女'), FOREIGN KEY(class...
CREATE TABLE employees ( id INT PRIMARY KEY, name VARCHAR(100), age INT CHECK (age >= 18 AND age <= 65), email VARCHAR(255) CHECK (email LIKE '%_@__%.__%') ); 参考链接 MySQL CHECK Constraint MySQL UNIQUE Constraint 通过以上信息,您可以更好地理解MySQL中CHECK约束的基础概念、优势、...
The FOREIGN KEY constraint works as it's supposed to, but the Gender field can be updated with any character, i.e., this INSERT statement works without errors: INSERT INTO Employees (EmployeeID, DepartmentID, FirstName, LastName, HomePhone, WorkPhone, Gender) ...
foreign key constraintfails(外键约束失败)(`atguigudb`.`emp`,CONSTRAINT`emp_ibfk_1`FOREIGNKEY(`deptid`)REFERENCES`dept`(`did`))//部门表did字段现在没有1002的值,所以员工 表中不能修改员工所在部门deptid为1002update deptsetdid=1002where did=1001;//修改主表失败ERROR1451(23000):Cannotdelete(删除) or...
CONSTRAINT <完整性约束条件名>[PRIMARY KEY短语 |FOREIGN KEY短语 |CHECK短语] 举个例子: [例10] 建立学生登记表Student,要求学号在90000~99999之间,姓名不能取空值,年龄小于30,性别只能是“男”或“女”。 CREATE TABLE Student (Sno NUMERIC(6) CONSTRAINT C1 CHECK (Sno BETWEEN 90000 AND 99999), Sname...
CONSTRAINT `t1_chk_4` CHECK ((`c1` > `c3`)) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci SQL规范要求:所有约束(包括:PRIMARY KEY,UNIQUE,FOREIGN KEY,CHECK)属于同一个命名空间(NAMESPACE),在MySQL实现中,所有的约束类型在每个schema (database)内有自己的命名空间。所以,CHE...
主键(primary key) 外键(foreign key):被参照的键必须有唯一约束或是主键 非空(not null) 默认(default) 检查(check):oracle独有 唯一(unique) 2. 六大约束的用法 以下所有演示的SQL语句都是基于Oracle,可能在MySQL中使用有些出入。不过不用担心,后面会指出一些MySQL与Oracle的不同之处 ...
Table pfs.metadata_locks fails for FOREIGN_KEY and CHECK_CONSTRAINT Submitted:29 Apr 2021 11:22Modified:10 May 2021 11:48 Reporter:Satya Bodapati(OCA)Email Updates: Status:ClosedImpact on me: None Category:MySQL Server: Performance SchemaSeverity:S2 (Serious)...
FOREIGN KEY [index_name] (index_col_name,...) reference_definition | [CONSTRAINT [symbol]] CHECK (condition) [[NOT] ENFORCED] ^^^ alter_specification: ... | ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (index_col_name,...) reference_definition | ADD [CONSTRAINT [symbol]] CHEC...