MySQL语法创建外键？
创建外键的语法如下-
alter table yourSecondTableName ADD CONSTRAINT yourConstraintname FOREIGN KEY(yourForeignKeyColumnName) references yourFirstTableName (yourPrimaryKeyColumnName);
为了理解上述语法，让我们创建两个表。创建第一个表的查询如下-
mysql> create table Department_Table -> ( -> Department_Id int not null auto_increment primary key, -> Department_Name varchar(30) -> );
创建第二张表的查询如下-
mysql> create table Employee_Table -> ( -> EmployeeID int not null auto_increment primary key, -> EmployeeName varchar(80), -> Job varchar(30), -> Department_Id int not null references department(departmentID) -> );
上面的Department_Idint而不是null引用department(departmentID)不会创建外键。现在，按照上述语法创建外键。
查询如下-
mysql> alter table Employee_Table ADD CONSTRAINT fk_Department_Id FOREIGN KEY(Department_Id) -> references Department_Table(Department_Id); Records: 0 Duplicates: 0 Warnings: