Question

不知道如何解决以下问题：

有三个表，每个表都有一列名称，例如

表1 - 列名称＆＃39;名称＆＃39; - 价值观＆＃39; A＆＃39;，＆＃39; B＆＃39;和＆＃39; C＆＃39;
表2 - 列名＆＃39;名称＆＃39; - 价值观＆＃39; A＆＃39;和＆＃39; B＆＃39;
表3 - 列nane＆＃39;名称＆＃39; - 价值观＆＃39; A＆＃39;和＆＃39; C＆＃39;

目标是UNION表 - 三个表的每个值只应显示一次。此外，应该有三个新的＆＃34;虚拟列＆＃34;显示包含值的表格（＆＃39; 1＆＃39;包含值时，＆＃39; 0＆＃39;如果不包含）。所以结果应该是这样的：

Value | Table1 | Table2 | Table3
--------------------------------
  A   |    1   |    1   |    1
  B   |    1   |    1   |    0
  C   |    1   |    0   |    1

希望有人可以帮助我，提前谢谢。

Answer 1

这样做你想要的吗？

select Name, max(Table1) as Table1, max(Table2) as Table2, max(Table3) as Table3
from (select Name, 1 as Table1, 0 as Table2, 0 as Table3
      from table1
      union all
      select Name, 0 as Table1, 1 as Table2, 0 as Table3
      from table2
      union all
      select Name, 0 as Table1, 0 as Table2, 1 as Table3
      from table3
     ) t
group by Name;

您可能希望使用sum()代替max()来获取每个表中值的出现次数。

Answer 2

这是我的尝试（更新：在SQL-Server 2005及以上版本中起作用，因为 CTE ）：

With names AS
(
   SELECT Name, Source = 'T1'
   FROM dbo.Table1

   UNION ALL

   SELECT Name, Source = 'T2'
   FROM dbo.Table2

   UNION ALL

   SELECT Name, Source = 'T3'
   FROM dbo.Table3
)
SELECT n.Name, 
       Table1 = CASE WHEN EXISTS
               (SELECT 1 FROM names n2 
                WHERE Source = 'T1' AND n2.Name=n.Name)
                THEN 1 ELSE 0 END,
       Table2 = CASE WHEN EXISTS
               (SELECT 1 FROM names n2 
                WHERE Source = 'T2' AND n2.Name=n.Name)
                THEN 1 ELSE 0 END,
       Table3 = CASE WHEN EXISTS
               (SELECT 1 FROM names n2 
                WHERE Source = 'T3' AND n2.Name=n.Name)
                THEN 1 ELSE 0 END
FROM names n
GROUP BY n.Name

Demo

Answer 3

如果您的数据库支持完全加入，您可以尝试以下查询。

select
  coalesce(t1.Name,t2.Name,t3.Name) myValue,
  (case when max(t1.Name) is not null then 1 else 0 end) c1,
  (case when max(t2.Name) is not null then 1 else 0 end) c2,
  (case when max(t3.Name) is not null then 1 else 0 end) c3
from
  Table1 t1 
  full join Table2 t2 on t1.Name = t2.Name
  full join Table3 t3 on t1.Name = t3.Name
group by coalesce(t1.Name,t2.Name,t3.Name)

如果您知道某个值在每个表格中不会出现多次，则可以删除group by和max部分。

联合三个表并显示数据来自何处

3 个答案: