加入两个不相关的表

Question

我有两个表，如A和B.每个表都有一个升序列（ID）。 我想加入表LIKE C表。数据不是静态的，但在A和B中，行数始终相等。我尝试过加入声明，但无法找到答案。谢谢你的帮助。

A (ID)
--
2
3
4
6
8

B (ID)
--
11
12
13
14
15

C ( IDA ,  IDB )
--
2     11
3     12
4     13
6     14
8     15

Answer 1

如果您正在使用支持row_number（）的数据库，例如Oracle，postgresql，sql sql server：

select a_id, b_id
  from (select row_number() over(order by id) as a_rn, id as a_id from a) x
  join (select row_number() over(order by id) as b_rn, id as b_id from b) y
    on x.a_rn = y.b_rn

小提琴： http://sqlfiddle.com/#!15/5ac6b/1/0

如果您正在使用mysql，则可以使用变量模拟row_number：

select a_id, b_id
  from (select @rn := @rn + 1 as a_rn, id as a_id
          from a
         cross join (select @rn := 0) r) x
  join (select @rx := @rx + 1 as b_rn, id as b_id
          from b
         cross join (select @rx := 0) r) y
    on x.a_rn = y.b_rn

小提琴： http://sqlfiddle.com/#!9/5ac6b/2/0

Answer 2

试试这个：

select a.id ida,b.id idb from 
( select a.*, row_number() over (order by id) rn from a) a
join (select b.*, row_number() over (order by id) rn from b) b on a.rn=b.rn

Answer 3

联接无关表

演示SQL脚本

IF OBJECT_ID('Tempdb..#T1') IS NOT NULL  DROP TABLE #T1;

CREATE TABLE #T1 (T1_Name VARCHAR(75));

INSERT INTO #T1 (T1_Name) VALUES ('Animal'),('Bat'),('Cat'),('Duet');

SELECT * FROM #T1;

IF OBJECT_ID('Tempdb..#T2') IS NOT NULL  DROP TABLE #T2;

CREATE TABLE #T2 (T2_Class VARCHAR(10));

INSERT INTO #T2 (T2_Class) VALUES ('Z'),('T'),('H'); 

SELECT * FROM #T2;

要联接不相关的表，我们将引入一个序列号的通用联接列，如下所示。

SQL脚本

SELECT T1.T1_Name,ISNULL(T2.T2_Class,'') AS T2_Class FROM
( SELECT T1_Name,ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS S_NO FROM #T1) T1
LEFT JOIN
( SELECT T2_Class,ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) AS S_NO FROM #T2) T2
ON t1.S_NO=T2.S_NO;