无法添加创建表MySQL的外键约束
方法无法添加创建表MySQL的外键约束,mysql,sql,minecraft,Mysql,Sql,Minecraft,方法createTable（）正在工作，我已经创建了其他简单的表，没有任何问题 我使用的是MySQL服务器8.0 这是对表的测试，然后我将制作一个脚本来创建它们。我一直有这样的错误： 无法创建表，SQLException:无法添加外键约束 但是我不知道怎么了 if(!database.checkTable("maps")){ String maps = "CREATE TABLE maps (" + "name VARCHAR(32) N
createTable（） if(!database.checkTable("maps")){
String maps = "CREATE TABLE maps ("
+ "name VARCHAR(32) NOT NULL,"
+ "mapType VARCHAR(32) NOT NULL,"
+ "world VARCHAR(32) NOT NULL,"
+ "referenceId INT(32) NOT NULL,"
+ "regionId INT(32) NOT NULL,"
+ "testmode BIT(1) NOT NULL,"
+ "edition BIT(1) NOT NULL,"
+ "finished BIT(1) NOT NULL,"
+ "PRIMARY KEY (name, referenceId, regionId))"
+ "ENGINE = InnoDB "
+ "DEFAULT CHARACTER SET = utf8;";
database.createTable(maps);
}
if(!database.checkTable("regions")){
String regions = "CREATE TABLE regions ("
+ "id INT(32) NOT NULL AUTO_INCREMENT,"
+ "minLocationId INT(32) NOT NULL,"
+ "maxLocationId INT(32) NOT NULL,"
+ "PRIMARY KEY (id, minLocationId, maxLocationId),"
+ "CONSTRAINT `regionMapFk`"
+ "FOREIGN KEY (id)"
+ "REFERENCES maps (regionId)"
+ "ON DELETE CASCADE "
+ "ON UPDATE CASCADE)"
+ "ENGINE = InnoDB "
+ "DEFAULT CHARACTER SET = utf8;";
database.createTable(regions);
}
if(!database.checkTable("locations")){
String locations = "CREATE TABLE locations ("
+ "id INT(16) NOT NULL AUTO_INCREMENT, "
+ "x INT(16) NOT NULL, "
+ "y INT(16) NOT NULL, "
+ "z INT(16) NOT NULL, "
+ "PRIMARY KEY(id),"
+ "CONSTRAINT `minLocationRegionFk`"
+ "FOREIGN KEY (id)"
+ "REFERENCES regions (minLocationId)"
+ "ON DELETE CASCADE "
+ "ON UPDATE CASCADE,"
+ "CONSTRAINT `maxLocationRegionFk`"
+ "FOREIGN KEY (id)"
+ "REFERENCES regions (maxLocationId)"
+ "ON DELETE CASCADE "
+ "ON UPDATE CASCADE,"
+ "CONSTRAINT `locationMapFk`"
+ "FOREIGN KEY (id)"
+ "REFERENCES maps (referenceId)"
+ "ON DELETE CASCADE "
+ "ON UPDATE CASCADE)"
+ "ENGINE = InnoDB "
+ "DEFAULT CHARACTER SET = utf8;";
database.createTable(locations);
}
我认为您正在反向创建外键，这是不正确的 由于您的
mapregionId外键，而不是在区域
本身。因此，在创建map
表的脚本中对其进行如下更改：
FOREIGN KEY (regionId) REFERENCES regions(id)
这同样适用于region
表的maxLocationId
列。外键应该在区域
表中定义，而不是在位置
本身中定义
任何外键都应该引用引用表中的主键
，否则mysql不会创建它
此外，在创建表和定义它们的主键，然后在它们之间创建任何引用外键时，应该保持依赖关系顺序
例如，您应该首先创建区域
表并定义其主键。之后，您应该创建您的映射
表，该表引用了区域
，现在您可以在映射
表中定义外键，该表引用了区域
表在其区域id
列上的id
（通常是主键）
有关创建外键的概念和语法，请参见参考。为什么在区域表中有外键（id）引用映射（regionId）？应该是另一种方式，不是吗（region表是主表，其id由表映射引用）
所以在createtablemapsddl中应该是这样的
FOREIGN KEY (regionId) REFERENCES region (id)
ON DELETE CASCADE
ON UPDATE CASCADE
与FK inside location table相同，我认为应该是另一种方式，即不能在一个表中创建多个主键
就像你们在地图桌上做的一样
"CREATE TABLE maps ("
+ "name VARCHAR(32) NOT NULL,"
+ "mapType VARCHAR(32) NOT NULL,"
+ "world VARCHAR(32) NOT NULL,"
+ "referenceId INT(32) NOT NULL,"
+ "regionId INT(32) NOT NULL,"
+ "testmode BIT(1) NOT NULL,"
+ "edition BIT(1) NOT NULL,"
+ "finished BIT(1) NOT NULL,"
+ "PRIMARY KEY (name, referenceId, regionId))"
+ "ENGINE = InnoDB "
+ "DEFAULT CHARACTER SET = utf8;";
要创建外键约束，您必须提供要绑定的表的主键的引用
CREATE TABLE Orders (
OrderID int NOT NULL,
OrderNumber int NOT NULL,
PersonID int,
PRIMARY KEY (OrderID),
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID)
);