TSQL加入查询

Question

Employee Table: 
Empid FNAme   LName  Hair Race 
1  john   adam  1  1 
2  clift   susanne 2  3 

Code Table: 
code type description 
1  hair black 
2  hair brown 
1  race black 
3  race white 

我们需要得到输出数据为empid, Fname, Lname, Hair, Race; 其中hair和race不作为代码显示，但描述形成代码表。

我初学者sql.Can请你帮忙写一个查询 我没有得到每一个期望的输出下面的查询

select E.Empid,E.FName,E.Lname,c.description as Hair,c.description as race 
From Employee2 E inner join code c 
on (c.code = E.Hair) 

Answer 1

你应该加入你的码表两次：

• 一次弄头发
• 一次拿到比赛

SQL语句

SELECT E.EmpID 
     , E.FName 
     , E.LName 
     , c1.Description AS Hair 
     , c2.Description AS Race 
FROM Employee E 
     INNER JOIN Code c1 ON c1.Code = e.Hair AND c1.type = 'hair' 
     INNER JOIN Code c2 ON c2.Code = e.Race AND c2.type = 'race' 

注意，如果其中一方可能是NULL，你想改变INNER JOIN到LEFT OUTER JOIN

---

说，我会建议你为头发和比赛创建一个单独的代码表。

试图将所有内容转储到一个代码表中只会让人们感到困惑，并且迫使您最好编写不理想的查询。您强制自己将该类型添加到代码表以及您将创建的每个连接中。

一个更好的选择将是

Employee Table: 
Empid FNAme   LName  Hair Race 
1  john   adam  1  1 
2  clift   susanne 2  3 

HairCode Table: 
code description 
1  black 
2  brown 

RaceCode Table: 
1  black 
3  white 

，并简化您的语句来

SELECT E.EmpID 
     , E.FName 
     , E.LName 
     , c1.Description AS Hair 
     , c2.Description AS Race 
FROM Employee E 
     INNER JOIN HairCode c1 ON c1.Code = e.Hair 
     INNER JOIN RaceCode c2 ON c2.Code = e.Race 

您将获得更好的性能和一个免费的占地面积更小。

Answer 2

你可以参加两次以获得您所需要

select E.Empid, E.FName, E.Lname, hair.description as Hair, race.description as race 
From Employee2 E 
inner join code hair on (hair.code = E.Hair and hair.type = 'hair') 
inner join code race on (race.code = E.Race and race.type = 'race')