There is already an object named '#columntable' in the database - sql

Question

I am trying the following query
if exists (select 1 from emp where eid = 6)
begin
if object_id('tempdb..#columntable') is not null
begin
drop table #columntable
end
create table #columntable (oldcolumns varchar(100))
end
else
begin
if object_id('tempdb..#columntable') is not null
begin
drop table #columntable
end
create table #columntable (newcolumns varchar(100))
end
But I am getting the error
Msg 2714, Level 16, State 1, Line 8
There is already an object named '#columntable' in the database.
Can anyone suggest why? The same query works fine if I do not write the else part.

Answer 1

This is a SQL Server parser error unfortunately (confirmed by Microsoft).
#DizGrizz is also right - SELECT .. INTO #SomeTable doesn't work if repeated in IF .. ELSE statements.
IF .. ELSE .. CREATE TABLE #SomeTempTable
In answer to the actual question, creating then altering the table works (you also only have to check and drop once)...
IF OBJECT_ID('tempdb..#MyTempTable') IS NOT NULL
BEGIN
DROP TABLE #MyTempTable
END
CREATE TABLE #MyTempTable (DummyColumn BIT)
IF EXISTS (SELECT 1 FROM EMP WHERE EID = 6)
BEGIN
ALTER TABLE #MyTempTable
ADD MyColumnType1 VARCHAR(100)
ALTER TABLE #MyTempTable
DROP COLUMN DummyColumn
END
ELSE
BEGIN
ALTER TABLE #MyTempTable
ADD MyColumnType2 VARCHAR(100)
ALTER TABLE #MyTempTable
DROP COLUMN DummyColumn
END
IF .. ELSE .. SELECT INTO #SomeTempTable
The issue I had however was the same as #DizGrizz: IF .. ELSE combined with SELECT .. INTO #SomeTable fails. As a workaround it's possible to select the top 0 rows (i.e. none) to create the table with the correct column types. (This insulates the script from column type changes and also avoids the pain of declaring every type.) INSERT INTO can then be used, provided IDENTITY_INSERT is set to ON to prevent errors:
IF OBJECT_ID('tempdb..#MyTempTable') IS NOT NULL
DROP TABLE #MyTempTable
-- This creates the table, but avoids having to declare any column types or sizes
SELECT TOP 0 KeyNm
INTO #MyTempTable
FROM dbo.MyDataTable2
-- Required to prevent IDENTITY_INSERT error
SET IDENTITY_INSERT #MyTempTable ON
IF #something = 1
BEGIN
-- Insert the actual rows required into the (currently empty) temp table
INSERT INTO #MyTempTable (KeyNm)
SELECT KeyNm
FROM dbo.MyDataTable2
WHERE CatNum = 2
END
ELSE
BEGIN
-- Insert the actual rows required into the temp table
INSERT INTO #MyTempTable (KeyNm)
SELECT KeyNm
FROM dbo.MyDataTable2
WHERE CatNum = 8
END
SET IDENTITY_INSERT #MyTempTable OFF

Answer 2

Temp tables are not dropped automatically at the end of a query, only when the current connection to the DB is dropped or you explicitly delete them with DROP TABLE #columntable
Either test for the existence of the table at the start of the query or alwayas delete it at the end (preferably both)
EDIT: As Matrin said in his comment, this is actually a parse error. You get the same error if you only parse the SQL as when you execute it.
To test that out I split up your query and tried:
if exists (select 1 from emp where id = 6)
create table #columntable (newcolumns varchar(100))
GO
if not exists (select 1 from emp where id = 6)
create table #columntable (oldcolumns varchar(100))
GO
The parser is happy with that. Interestingly if you change to using non-temp tables the original query parses fine (I realise the problems that would create, I was just interested to find out why the query would not parse).

Answer 3

This also occurs if you create the tables with SELECT INTO...as in
IF OBJECT_ID('tempdb..#MyTempTable', 'U') IS NOT NULL
DROP TABLE #MyTempTable
SELECT TOP 1 #MyVariable = ScaleValue
FROM MyDataTable1
WHERE ProductWeight > 1000
IF #MyVariable = 1
BEGIN
SELECT KeyNm
INTO #MyTempTable
FROM dbo.MyDataTable2
WHERE CatNum = 2
END
ELSE
BEGIN
SELECT KeyNm
INTO #MyTempTable
FROM dbo.MyDataTable2
WHERE CatNum = 8
END
The parser should not even attempt to detect this because, in many cases, it would be impossible for the parser to determine if the table would already exist. The code above is a perfect example...there would be no way for the parser to determine the value of #MyVariable.
I hope that someone has informed MS of this bug (I don't have their ear).

Answer 4

You can check if it exists by doing:
IF OBJECT_ID('tempdb..#columntable') IS NOT NULL
BEGIN
DROP TABLE #columntable
PRINT 'Dropped table...'
END

Answer 5

Use global temp tables and wrap the select in exec.
Example:
Fail
declare #a int = 1
if object_id('tempdb..##temp') is not null drop table ##temp
if(#a = 1) select * into ##temp from table_1
else if(#a = 2) select * into ##temp from table_2
Win
declare #a int = 1
if object_id('tempdb..##temp') is not null drop table ##temp
if(#a = 1) exec('select * into ##temp from table_1')
else if(#a = 2) exec('select * into ##temp from table_2')
This will fool the buggy parser that is trying to be smarter than it is.
And Microsoft - please fix this.

Answer 6

The error is wrong, remove the if clause and it runs through fine. Thus the problem is in the exists:
if object_id('tempdb..#columntable') is not null
begin
drop table #columntable
end
create table #columntable (oldcolumns varchar(100))

Answer 7

Well I got the answer...
As Martin said this is a parse/compile issue. So I Tried changing my script as below
if exists (select 1 from emp where eid = 6)
begin
if object_id('tempdb..#columntable') is not null
begin
drop table #columntable
end
create table #columntable (oldcolumns varchar(100))
end
go
if exists (select 1 from emp where eid = 1)
begin
if object_id('tempdb..#columntable') is not null
begin
drop table #columntable
end
create table #columntable (newcolumns varchar(100))
end
And this worked for me.

Answer 8

I have been experiencing this issue. My query consisted of several joined SELECT statements in the form of:
DROP TABLE IF EXISTS ##TempTableName
SELECT statement ...
So, every time I tried to alter SQL code I would get the above error. I have changed all my temp tables from ##global to #local and now I am able to alter my SQL as many times as needed. So the example above would become:
DROP TABLE IF EXISTS #TempTableName
SELECT statement ...