正确的SQL数据表查询写

Question

我有一个表t1与三列id，c1，c2，c3与特定数字。我有一个不同的表t2与id，名称其中id值是c1，c2，c3的值。

我无法写一个查询，我可以得到结果为

id | c1 |的名称c2的名称| c3的名字

有人可以帮忙。

Answer 1

一种方式是写子查询检索每个列的名称：

select t1.id 
,  (select name from t2 where t2.id = t1.c1) as C1Name 
,  (select name from t2 where t2.id = t1.c2) as C2Name 
,  (select name from t2 where t2.id = t1.c3) as C3Name 
from t1 

或者你可以使用一个牛肚加入：

select t1.id 
,  t2_1.name as C1Name 
,  t2_2.name as C2Name 
,  t2_3.name as C3Name 
from t1 
join t2 as t2_1 on t1.c1 = t2_1.id 
join t2 as t2_2 on t1.c2 = t2_2.id 
join t2 as t2_3 on t1.c3 = t2_3.id 

Answer 2

你需要在每个加入三次的价值来获得他们的名字。

SELECT T1.id, FirstJoin.Name, SecondJoin.Name, ThirdJoin.Name FROM T1 
JOIN T2 FirstJoin On T1.c1 = FirstJoin.Id 
JOIN T2 SecondJoinOn T1.c2 = SecondJoin.Id 
JOIN T2 ThirdJoinOn T1.c3 = ThirdJoin.Id 

我为蹩脚的别名道歉。

Answer 3

SELECT 
    t1.id, 
    sub1.name, 
    sub2.name, 
    sub3.name 
FROM 
    t1 
     JOIN t2 AS sub1 ON t1.c1 = sub1.id 
     JOIN t2 AS sub2 ON t1.c2 = sub2.id 
     JOIN t2 AS sub3 ON t1.c3 = sub3.id; 

但是，你应该修复你的数据模型，3列与相同类型的数据，听起来像一个坏的datamodel。做一些正常化。