如何在 MySQL DB 中识别外键?
mysqlmysqli database
首先我们创建一个表 −
mysql> create table DemoTable1 (Id int NOT NULL PRIMARY KEY,EmployeeName varchar(100)); Query OK, 0 rows affected (0.50 sec)
以下是创建具有外键约束的第二个表的查询−
mysql> create table DemoTable2 ( Id int NOT NULL, StreetName varchar(100), CityName varchar(100), CountryName varchar(100), PinCode int, EmployeeId int, PRIMARY KEY(Id), FOREIGN KEY (Id) REFERENCES DemoTable1(Id) ); Query OK, 0 rows affected (0.46 sec)
以下是识别 MySQL DB 中外键的查询 −
mysql> show create table DemoTable2\G
这将产生以下输出 −
*************************** 1. row *************************** Table: DemoTable2 Create Table: CREATE TABLE `demotable2` ( `Id` int(11) NOT NULL, `StreetName` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL, `CityName` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL, `CountryName` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL, `PinCode` int(11) DEFAULT NULL, `EmployeeId` int(11) DEFAULT NULL, PRIMARY KEY (`Id`), CONSTRAINT `demotable2_ibfk_1` FOREIGN KEY (`Id`) REFERENCES `demotable1` (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci 1 row in set (0.00 sec)
