Question

我有一张桌子

CREATE TABLE IF NOT EXISTS `hrms_employee_leave` (
`employee_leave_id` int(11) NOT NULL,
 `employee_id` int(11) NOT NULL,
`leave_category_id` int(11) NOT NULL,
`days` int(11) NOT NULL
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1;

它会显示员工有多少请假，这是此表中的数据存储。

Employee_id = 25, 
leave_category_id = 2, 
days = 14

Employee_id = 25,
leave_category_id = 3,
days = 14

当我内部加入表格时，输出就像

Employee Name = Foo,
Leave Category = Annual Leave,
days = 14
Foo has 14 days of Annual Leave.

Employee Name = Foo,
Leave Category = Medical Leave,
days = 14
Foo has 14 days of Medical Leave.

如何合并 employee_id 和 leave_category_id 成为无法复制的唯一键，以防止用户插入多次

Employee_id = 25, 
leave_category_id = 2, 
days = 14

Employee_id = 25,
leave_category_id = 3,
days = 14

Answer 1

添加多列唯一索引有多种方法。例如。你可以在create table语句中执行它：

CREATE TABLE IF NOT EXISTS `hrms_employee_leave` (
`employee_leave_id` int(11) NOT NULL,
 `employee_id` int(11) NOT NULL,
`leave_category_id` int(11) NOT NULL,
`days` int(11) NOT NULL,
  CONSTRAINT `uniqueindex_1` UNIQUE (`employee_leave_id`, `leave_category_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1;

这样，emloyee_leave_id和leave_category_id 组合不会重复。而且，这些都不是NULL。如果这些列同时可以是外键，则两者都可以。

请参阅示例，其中这两列既是外键又是复合唯一索引：http://www.sqlfiddle.com/#!9/a4dfc

如何将2个外键组合为唯一键并且不能复制

1 个答案: