Question

我有一个要求，当ID都相同时，我需要显示两个表的数据。当第一个表中存在id而第二个表中没有id时，我需要显示第一个表中的数据

CREATE TABLE [dbo].[TEST](
    [ID] [int] NULL,
    [Name] [varchar](10) NULL,
    [Status] [char](1) NULL,
    [CreatedDate] [datetime] NULL
) ON [PRIMARY]

GO

CREATE TABLE [dbo].[Test_History](
    [ID] [int] NULL,
    [Name] [varchar](10) NULL,
    [Status] [char](1) NULL,
    [CreatedDate] [datetime] NULL
) ON [PRIMARY]

GO
/****** Object:  Table [dbo].[Test_History]    Script Date: 06/19/2015 19:01:49 ******/
INSERT [dbo].[Test_History] ([ID], [Name], [Status], [CreatedDate]) VALUES (1, N'Mohan', N'A', CAST(0x0000A4BC01347E88 AS DateTime))
INSERT [dbo].[Test_History] ([ID], [Name], [Status], [CreatedDate]) VALUES (1, N'Mohan', N'I', CAST(0x0000A4BC0134A390 AS DateTime))
INSERT [dbo].[Test_History] ([ID], [Name], [Status], [CreatedDate]) VALUES (2, N'Rohan', N'A', CAST(0x0000A4BC01391FCC AS DateTime))
/****** Object:  Table [dbo].[TEST]    Script Date: 06/19/2015 19:01:49 ******/
INSERT [dbo].[TEST] ([ID], [Name], [Status], [CreatedDate]) VALUES (2, N'Rohan', N'I', CAST(0x0000A4BC0138D584 AS DateTime))
INSERT [dbo].[TEST] ([ID], [Name], [Status], [CreatedDate]) VALUES (1, N'Mohan', N'A', CAST(0x0000A4BC013072DC AS DateTime))
INSERT [dbo].[TEST] ([ID], [Name], [Status], [CreatedDate]) VALUES (3, N'Raj', N'A', CAST(0x0000A4BC0138DED7 AS DateTime))
INSERT [dbo].[TEST] ([ID], [Name], [Status], [CreatedDate]) VALUES (4, N'Krishna', N'A', CAST(0x0000A4BC0138EE31 AS DateTime))

到目前为止，我已经尝试了我的查询来实现结果

select T.ID,COALESCE(T.ID,TT.ID),T.Name,COALESCE(T.Name,TT.Name),T.status,COALESCE(T.status,TT.status)

 from Test T LEFT JOIN (Select TOP 1  ID,MIN(Name)name,Status from Test_History
 GROUP BY  ID,status
 )TT
 ON T.ID = TT.ID

 where T.ID = 3

    Id = 1 and 2 present show i will get data from both tables 
    Id = 3 and 4 not present in the table 
so using coalesce i will get the data

从第一个表开始，并在第二个表列中显示

但是还有其他任何方式，比如两个表都是相同的结构

我在考虑

Declare @tablename varchar(10)
IF EXISTS (SELECT 1 from TESt where id = @id)
IF COunt there in both tables 
SET @tablename = Test 
ELSE 
SET @tablename = Test_history

select * from @tablename  where id = @ID

我可以得到像这样的任何解决方案

Answer 1

首先：感谢您对问题相关数据的出色设置！

如果你真正的问题是如果你的问题中描述的表变量可以使用，答案是否定的;或者更确切地说，它不值得。

不推荐：

declare @TableName TABLE (
[ID] [int] NULL,
[Name] [varchar](10) NULL,
[Status] [char](1) NULL,
[CreatedDate] [datetime] NULL)

IF EXISTS (SELECT 1 from TESt where id = @id)
    INSERT INTO @TableName SELECT * FROM dbo.TEST WHERE ID = @ID
ELSE INSERT INTO @TableName SELECT * FROM dbo.[Test_History] WHERE ID = @ID 

select * from @tablename  where id = @ID

以下是我更喜欢的解决方案：

DECLARE @ID INT = 3;
SELECT * FROM [dbo].[TEST]  ss WHERE ss.id = @id
UNION ALL SELECT * FROM [dbo].[Test_History] th WHERE th.id = @id
  and not exists ( SELECT * FROM [dbo].[TEST]  ss WHERE ss.id = @id);

UNION ALL效果非常好 - 不要忘记ALL关键字，我假设ID是PK或AK。

Answer 2

您可以使用EXCEPT。

以下是一个例子：

SELECT a,b 
FROM (
    VALUES (1, 2), (3, 4), (5, 6), (7, 8), (9, 10)
) AS MyTable(a, b)
EXCEPT
SELECT a,b
FROM (
    VALUES (1, 2),  (7, 8), (9, 10)
) AS MyTable(a, b);

这将返回upper语句的所有行，这些行不在第二个语句中。

Answer 3

如果我理解正确并且您希望显示两个表之间匹配的所有记录，并且只显示同一结果集中第二个表中不存在id的第一个表中的记录，那么您只需要一个简单的左连接：

SELECT * 
FROM dbo.test t
LEFT OUTER JOIN Test_History th 
    ON t.id = th.id
WHERE t.id = @id

当第二个表中没有数据时，如何从第一个表获取表

3 个答案: