根据 SQL Server 中表中的列值从两个表中获取一个新表：

Posted 2023-03-31

【中文标题】根据 SQL Server 中表中的列值从两个表中获取一个新表：

【英文标题】：get a new table from two tables based on the columns' values in a table in SQL server:

【发布时间】：2016-02-23 22:34:36

【问题描述】：

我需要从 SQL server 的两个表中获取一个新表：

tbl1：

id value
1  abc
2  abd
3  dft

tbl2：

num  abc  abd  dft   
1    5     9   0       
2    8     0   7        

如果 tbl2 中的列不为 0，则从 tbl1 中获取 id，如：

 num   id
 1     1  (abc <> 0 in tbl2)    
 1     2  (abd <> 0 in tbl2)    
 2     1  (abc <> 0 in tbl2)     
 2     3  (dft <> 0 in tbl2)      

我的 SQL 查询：

 select tbl2.num, case when (tbl2.abc != 0 ) then select tbl1.id from tbl1 end as id
 from tbl2, tbl1

但是，这不是我想要的。我不想使用循环来做到这一点。

谢谢！

【问题讨论】：

您需要加入表格，而不仅仅是列出它们。

【参考方案1】：

我想你想要union all:

select num, 1 as id from tbl2 where abc <> 0
union all
select num, 2 as id from tbl2 where abd <> 0
union all
select num, 3 as id from tbl2 where dft <> 0;

如果你想从第一个表中获取 id：

select t2.num, t1.id
from tbl2 cross join
     (select id from tbl1 where value = 'abc') t1
where abc <> 0
union all
select num, t1.id
from tbl2 cross join
     (select id from tbl1 where value = 'abd') t1
where abd <> 0
union all
select num, t1.id
from tbl2 cross join
     (select id from tbl1 where value = 'dft') t1
where dft <> 0;

【参考方案2】：

你可以像这样使用 unpivot：

;WITH tbl1 AS (
SELECT * FROM (VALUES 
(1, 'abc'),
(2, 'abd'),
(3, 'dft')) as t1(id, value)
)
,tbl2 AS (
SELECT * FROM (VALUES 
(1, 5, 9, 0),
(2, 8, 0, 7)) as t2(num, abc, abd, dft)
)

--Unpivot the table.
SELECT num, tbl1.id
FROM 
   (SELECT num, 
            CASE WHEN abc != 0 THEN 1 ELSE NULL END as abc,
            CASE WHEN abd != 0 THEN 1 ELSE NULL END as abd,
            CASE WHEN dft != 0 THEN 1 ELSE NULL END as dft
   FROM tbl2) p
UNPIVOT
   (value FOR id IN 
      (abc, abd, dft)
)AS unpvt
LEFT JOIN tbl1 on tbl1.value = unpvt.id

结果：

num         id
----------- -----------
1           1
1           2
2           1
2           3