PRIMARY KEY (PK) 标识该字段为该表的主键,可以唯一的标识记录 FOREIGN KEY (FK) 标识该字段为该表的外键 NOT NULL 标识该字段不能为空 UNIQUE KEY (UK) 标识该字段的值是唯一的 AUTO_INCREMENT 标识该字段的值自动增长(整数类型,而且为主键) DEFAULT 为该字段设置默认值 UNSIGNED 无符号 ZEROFILL 使用0填充...
字段2 数据类型,[CONSTRAINT<外键约束名称>]FOREIGN KEY(从表的某个字段)references 主表名(被参考字段));//(从表的某个字段)的数据类型必须与主表名(被参考字段)的数据类型一致,逻辑意义也一样 //(从表的某个字段)的字段名可以与主表名(被参考字段)的字段名一样,也可以不一样 1. 2. 3. 4. 5. 6...
CONSTRAINT `sc_ibfk_2` FOREIGN KEY (`cno`) REFERENCES `course` (`cno`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | 这个关键字 CONSTRAINT 后面的就是这个约束的名字,然后就可以删除了,下面给出删除和添加的示例 mysql>alter table sc drop foreign key sc_ibfk_1; Query OK,0rows affected (0.03sec) R...
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)...
以下是一个简单的示例,展示如何在MySQL中使用CHECK约束: 代码语言:txt 复制 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 <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...
Sometimes foreign-key integrity will be violated, as a result of operating with @@foreign_key_checks = 0, ALTER ... NOCHECK, storage engine failure, etc. So MySQL should have a standard way to check whether all is well. The original suggestion in WL#148 was: " CHECK TABLE --- It is...
To create a CHECK constraint on the "Age" column when the table is already created, use the following SQL:ALTER TABLE Persons ADD CHECK (Age>=18); To allow naming of a CHECK constraint, and for defining a CHECK constraint on multiple columns, use the following SQL syntax:...
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...
CONSTRAINT `t1_chk_4` CHECK ((`c1` > `c3`)) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci The SQL standard specifies that all types of constraints (primary key, unique index, foreign key, check) belong to the same namespace. In MySQL, each constraint type has...