Question

我有一个表t1，其中有三列id，c1，c2，c3，带有一些数字。我有一个不同的表t2，其中包含id，name，其中id中的值是c1，c2，c3的值。

我无法编写查询，我可以将结果作为

id | c1的名字c2的名字c3的名字

有人可以提供帮助吗。

Answer 1

一种方法是编写子查询以检索每列的名称：

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tripe join：

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

您需要在每个值上加入三次以获取其名称。

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

我为蹩脚的走样道歉。

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;

但你应该修复你的数据模型，3列具有相同类型的数据，听起来像一个糟糕的数据模型。做一些规范化。

正确的SQL数据表查询编写

3 个答案: