SQL在If和Else块中插入临时表

Posted 2021-05-04

我正在尝试根据SQL 2005中的条件结果填充临时表。临时表将具有相同的结构，但将根据条件使用不同的查询填充。以下简化的示例脚本在ELSE块INSERT INTO的语法检查中失败，错误为：

数据库中已经有一个名为“#MyTestTable”的对象。

DECLARE @Id int
SET @Id = 1

IF OBJECT_ID('tempdb..#MyTestTable') IS NOT NULL DROP TABLE #MyTestTable

IF (@Id = 2) BEGIN 
    SELECT 'ABC' AS Letters
    INTO #MyTestTable;
END ELSE BEGIN
    SELECT 'XYZ' AS Letters
    INTO #MyTestTable;
END

我可以在IF/ELSE语句之前创建临时表，然后在条件块中执行INSERT SELECT语句，但该表将有很多列，我试图提高效率。这是唯一的选择吗？或者有一些方法可以使这项工作？

谢谢，马特

答案

您遇到的问题不是您正在填充临时表，而是您正在尝试创建表。 SQL会解析您的脚本并发现您尝试在两个不同的位置创建它，因此会引发错误。要意识到“执行路径”不可能同时触及两个创建状态，这并不够聪明。使用动态SQL将无法正常工作;我试过了

DECLARE @Command  varchar(500)

DECLARE @Id int 
SET @Id = 2

IF OBJECT_ID('tempdb..#MyTestTable') IS NOT NULL DROP TABLE #MyTestTable 

IF (@Id = 2) BEGIN  
    SET @Command = 'SELECT ''ABC'' AS Letters INTO #MyTestTable'
END ELSE BEGIN 
    SET @Command = 'SELECT ''XYZ'' AS Letters INTO #MyTestTable'
END 

EXECUTE (@Command)

select * from #MyTestTable

但临时表只持续动态会话。所以，唉，看起来你必须首先声明表然后填充它。也许是编写和支持的笨拙代码，但它会足够有效地执行。

另一答案

回答迟了8年，但我很惊讶没人想到：

select * into #MyTempTable from...
where 1=2

IF -- CONDITION HERE
insert into #MyTempTable select...
ELSE
insert into #MyTempTable select...

简单，快速，而且有效。不需要动态sql

另一答案

在您提供的方案中，您可以执行此操作

DECLARE @Id int
SET @Id = 1

IF OBJECT_ID('tempdb..#MyTestTable') IS NOT NULL DROP TABLE #MyTestTable

SELECT 
  CASE WHEN (@Id = 2) 
    THEN 'ABC' 
    ELSE 'XYZ' 
  END AS Letters
INTO #MyTestTable;

但是否则你需要在if statement之前创建这样的表

Create Table #MyTestTable (
  MyValue varchar(3)
)
IF (@Id = 2) BEGIN 
  Insert Into (MyValue)
  SELECT 'ABC' AS Letters;
END ELSE BEGIN
  Insert Into (MyValue)
  SELECT 'XYZ' AS Letters;
END

另一答案

如果临时表不能预先创建并且不希望将核心逻辑放在动态SQL中，那么我使用这个解决方案。

IF 1 = 1 -- Replace with actual condition
BEGIN
    SELECT * INTO #tmp1 FROM dbo.Table1
END
ELSE
BEGIN
    SELECT * INTO #tmp2 FROM dbo.Table2
END

-- Inserting data into global temp table so sql server can't complain on not recognizing in a context
DECLARE @Command VARCHAR(MAX)
IF OBJECT_ID('tempdb..#tmp1') IS NOT NULL
BEGIN
    SET @Command = 'SELECT * INTO ##tmp FROM #tmp1'
END
ELSE
BEGIN
    SET @Command = 'SELECT * INTO ##tmp FROM #tmp2'
END

EXECUTE(@Command)
SELECT * INTO #tmpFinal FROM ##tmp -- Again passing data back to local temp table from global temp table to avoid seeing red mark

IF OBJECT_ID('tempdb..##tmp') IS NOT NULL DROP TABLE ##tmp
IF OBJECT_ID('tempdb..#tmp1') IS NOT NULL DROP TABLE #tmp1
IF OBJECT_ID('tempdb..#tmp2') IS NOT NULL DROP TABLE #tmp2

SELECT * FROM #tmpFinal

IF OBJECT_ID('tempdb..#tmpFinal') IS NOT NULL DROP TABLE #tmpFinal

另一答案

这是一个老问题，但对于其他人来到这里：

用户Philip Kelley给出的动态SQL答案不适用于本地临时表（#Mytemp）。您可以做的是创建动态SQL以将其插入到全局临时表（##MyTemp）中，以后可以将其删除。

DECLARE @Command  varchar(500)

DECLARE @Id int 
SET @Id = 2

IF OBJECT_ID('tempdb..#MyTestTable') IS NOT NULL DROP TABLE ##MyTestTable 

IF (@Id = 2) BEGIN  
    SET @Command = 'SELECT ''ABC'' AS Letters INTO ##MyTestTable'
END ELSE BEGIN 
    SET @Command = 'SELECT ''XYZ'' AS Letters INTO ##MyTestTable'
END 

EXECUTE (@Command)

select * from ##MyTestTable

DROP ##MyTestTable

另一答案

这段代码可以帮到你

--creating temptable using columns of two existing tables
--you can create your temp table Using other methods

select top 0 VI.*,VU.FullName
into #mytemptable
from dbo.Items VI inner join
     dbo.Users as VU 
     on VU.Id=VI.Id

--insert your data base on your condition
if(i<2) --First Condition
begin
INSERT INTO #mytemptable
SELECT VI.*,VU.FullName 
from dbo.Items VI inner join
     dbo.Users as VU 
     on VU.Id=VI.Id
end
Else if(2<i) --Second Condition
begin
INSERT INTO #mytemptable
SELECT VI.*,VU.FullName 
from dbo.Items VI inner join
     dbo.Users as VU 
     on VU.Id=VI.Id
end

select * from #mytemptable --show result

drop table #mytemptable --drop table if its needed

此代码适用于sql server 2014我不知道它是否适用于sql 2005

另一答案

我试过这个：

SELECT S1.* INTO #MytestTable
FROM 
(   SELECT 'ABC' AS Letters WHERE 1 = CASE @Id=2 THEN 1 ELSE 2 END
    UNION
    SELECT 'XYZ' AS Letters WHERE 1 = CASE @Id=1 THEN 1 ELSE 2 END
) AS S1

如果以后需要向#MyTestTable添加列，这个解决方案会更好，因为否则您必须在重新运行脚本之前将其删除，这在测试条件下很烦人。

另一答案

在两种情况下，您可以在选择INTO之前删除该表。例如：

DECLARE @Id int 
SET @Id = 1  

IF (@Id = 2) BEGIN  
    IF OBJECT_ID('tempdb..#MyTestTable') IS NOT NULL DROP TABLE #MyTestTable
    SELECT 'ABC' AS Letters 
    INTO #MyTestTable; 
END ELSE BEGIN 
    IF OBJECT_ID('tempdb..#MyTestTable') IS NOT NULL DROP TABLE #MyTestTable 
    SELECT 'XYZ' AS Letters 
    INTO #MyTestTable; 
END 

评论后更新：

那很烦人。

两个单独的临时表怎么样？然后在If / Else登录后，检查每个是否存在，如果存在，选择第三个临时表？这可能不会很好，但是否重要取决于你需要什么。