創(chuàng)建外鍵的語法如下-alter?table?yourSecondTableName?ADD?CONSTRAINT?yourConstraintname?FOREIGN?KEY(yourForeignKeyColumnName)

references?yourFirstTableName?(yourPrimaryKeyColumnName);

為了理解上述語法，讓我們創(chuàng)建兩個(gè)表。創(chuàng)建第一個(gè)表的查詢?nèi)缦?mysql>?create?table?Department_Table

->?(

->?Department_Id?int?not?null?auto_increment?primary?key,

->?Department_Name?varchar(30)

->?);

創(chuàng)建第二張表的查詢?nèi)缦?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_Id int而不是null引用department(departmentID)不會(huì)創(chuàng)建外鍵。現(xiàn)在，按照上述語法創(chuàng)建外鍵。

查詢?nèi)缦?mysql>?alter?table?Employee_Table?ADD?CONSTRAINT?fk_Department_Id?FOREIGN?KEY(Department_Id)

->?references?Department_Table(Department_Id);

Records:?0?Duplicates:?0?Warnings:

總結(jié)

以上是生活随笔為你收集整理的mysql基本语法 外键_MySQL语法创建外键？的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。