c# - 如何为员工表中的记录分配唯一标识符？

Question

我知道这是第一个标准问题，但有人问我，但我无法给他适当的答案。有两个表在.Employee 表中Employee,Technology保存了多对多关系，其中包含字段，其中技术具有字段， 这两个表允许名称重复。我应该定义哪个唯一约束以允许唯一条目？employee_technology_relemp_id (auto_increment)emp_name(varchar)DOB (date)tech_id(auto_increment)tech_name(varchar)

Answer 1

You can define the unique entry on table employee_technology_rel,

ALTER TABLE employee_technology_rel 
       ADD CONSTRAINT emptech_pk PRIMARY KEY (emp_id, tech_id)
// or if you have set a primary key already, you can still define via UNIQUE
ALTER TABLE employee_technology_rel 
       ADD CONSTRAINT emptech_uq UNIQUE (emp_id, tech_id)

what it does is it only allows unique technology for every employee.

in order for you to have unique emp_name on table Employee as well as unique tech_name on table Technology, you can also alter the table by adding unique constraint

ALTER TABLE Employee ADD CONSTRAINT emp_uq UNIQUE (emp_name)
ALTER TABLE Technology ADD CONSTRAINT tech_uq UNIQUE (tech_name)

Answer 2

You want a composite primary key defined on the two columns in employee_technology_rel: emp_id and tech_id.

Answer 3

唯一索引和唯一约束相同。他们达到相同的目标。两者的 SQL 性能相同。

添加唯一约束 ALTER TABLE dbo。在 [PRIMARY] 上添加约束唯一非聚集 ( )

在 dbo 上添加唯一索引 CREATE UNIQUE NONCLUSTERED INDEX。( ) 开 [主要]

来源sqlauthority.com和msdn来自 Google 搜索：“ SQL 服务器唯一索引”。