Union All 但只保留 T-SQL 中一个 table 的重复项

Question

我有两个 table 我想合并。我只需要保留两个 table 之一的重复项。我试图找到它，但找不到任何地方。希望有人能帮忙。

例如： Table_1:

ID	Product	Amount
1	A	10
2	B	10
3	C	10

Table_2:

ID	Product	Amount
3	C	9
4	A	100
5	B	100

想要的结果：

ID	Product	Amount
1	A	10
2	B	10
3	C	9
4	A	100
5	B	100

因此请始终使用 table_2 中的重复项。在此示例中，ID 3 是重复的，因此使用 table_2 的副本，数量为 9.

如何用T-SQL实现这个？我使用了下面的代码：

Select * from Table_1 where Table_1.id != Table_2.id
Union All
Select * from Table_2

但随后我收到错误消息： 'The multi-part identifier "Table_2.ID" could not be bound.'

Answer 1

使用not exists:

Select t1.*
from Table_1 t1
where not exists (select 1 from table_2 t2 where t2.id = t1.id)
Union All
Select t2.*
from Table_2 t2;

Answer 2

我假设你想要的是 EXISTS:

SELECT T1.ID,
       T1.Product,
       T1.Amount
FROM dbo.Table1 T1
WHERE NOT EXISTS (SELECT 1
                  FROM dbo.Table2 T2
                  WHERE T1.ID = T2.ID)
UNION ALL
SELECT T2.ID,
       T2.Product,
       T2.Amount
FROM dbo.Table2 T2;

A FULL OUTER JOIN，但是，也可能有效如果 ID 在两个表中都是唯一的：

SELECT ISNULL(T2.ID,T1.ID) AS ID,
       ISNULL(T2.Product,T1.Product) AS Product,
       ISNULL(T2.Amount,T1.Amount) AS Amount
FROM dbo.Table1 T1
     FULL OUTER JOIN dbo.Table2 T2 ON T1.ID = T2.ID;

Answer 3

联盟会给你结果。 Union 总是 return 唯一值。如果您使用 union all ，您将获得所有重复项。您的答案是使用 union all。

  SELECT 
  B.ID
 ,B.Product
 ,B.Amount
 FROM
   (

    SELECT 
      A.ID
     ,A.Product
     ,A.Amount
     ,ROW_NUMBER() over (Partition BY  ID, Product order by  Amount ASC) AS [row_num]
    FROM
    (
       SELECT 
          tb_1.*
       FROM tb_1
       UNION ALL 
      SELECT 
        tb_2.* 
      FROM tb_2

     ) AS A
  ) AS B
  WHERE B.[row_num] = 1

Answer 4

试试这个：

SELECT  T1.*
FROM    @Table1 T1
WHERE   T1.ID NOT IN (SELECT ID FROM @Table2)
UNION
SELECT  T2.*
FROM    @Table2 T2

Union All 但只保留 T-SQL 中一个 table 的重复项

Union All but keep only duplicates from one table in T-SQL

sql

tsql

sql-server

union

union-all