How to set data to a variable from temporary table? - sql-server-2008

Question

I have declared a temporary table
DECLARE #Table Table
(
ID INT IDENTITY(1,1),
TableColumn VARCHAR(MAX)
)
DECLARE #Temp VARCHAR(MAX)
SET #Temp='SELECT * FROM '+'#Table'+''
SELECT #Temp
EXEC (#Temp)
I want to set all data of #Table to a variable #Temp. The above I tried practice is correct? Presently it shows some error.
Msg 1087, Level 15, State 2, Line 1
Must declare the table variable "#Table".
I tried in the above methode then it shows error like
Msg 156, Level 15, State 1, Line 1
Incorrect syntax near the keyword 'AS'.
Msg 1087, Level 15, State 2, Line 9
Must declare the table variable "#Table". Msg 139, Level 15, State 1,
Line 0
Cannot assign a default value to a local variable.
Msg 137, Level 15, State 2, Line 17
Must declare the scalar variable "#Temp".

Answer 1

This is to show the difference between a table variable and a temp table. You can't do what you are trying to do. Also, #temp is just a variable to contain the SQL you want to execute. If you want the results in another variable, another will have to be declared.
DECLARE #Table TABLE (
ID INT IDENTITY(1, 1)
,TableColumn VARCHAR(MAX)
)
INSERT INTO #Table (TableColumn)
VALUES ('testing 1,2,3')
SELECT *
FROM #table --with table variables, you can only select in the scope
DECLARE #Temp VARCHAR(MAX)
SET #Temp = 'SELECT * FROM #Table'
BEGIN TRY
--SELECT #Temp
EXEC (#Temp) --fails, because #table is not in scope
END TRY
BEGIN CATCH
SELECT 'Table variable dynamic execution failed'
END CATCH
GO
CREATE TABLE #table (
ID INT IDENTITY(1, 1)
,TableColumn VARCHAR(MAX)
)
INSERT INTO #Table (TableColumn)
VALUES ('testing 1,2,3')
DECLARE #Temp VARCHAR(MAX)
SET #Temp = 'SELECT * FROM #Table' --you can select out of a temp table with dynamic sql, because it will remain in scope for called procedures
--SELECT #Temp
EXEC (#Temp)
DROP TABLE #table

Answer 2

EXEC() creates new context, variables are not visible there so you need to pass them as argument. But temp table and normal tables are visible. This is why you get
Must declare the table variable "#Table".
If you can change temp variables to temp tables.
SqlFiddleDemo
CREATE TABLE #Table
( ID INT IDENTITY(1,1),
TableColumn VARCHAR(MAX));
INSERT INTO #Table
VALUES ('aaa'), ('bbb');
DECLARE #Temp NVARCHAR(MAX) ='SELECT * FROM <placeholder>';
SET #Temp = REPLACE(#Temp, '<placeholder>', '#Table');
-- SELECT #Temp;
EXEC [dbo].[sp_executesql]
#Temp;
If you want to query temp variables you need to create table type and pass to dynamic sql as argument like:
Demo
CREATE TYPE MyTable AS TABLE
(
ID INT IDENTITY(1,1),
TableColumn VARCHAR(MAX)
);
DECLARE #Table AS MyTable;
INSERT INTO #Table
VALUES ('aaa'), ('bbb');
DECLARE #Temp NVARCHAR(MAX) ='SELECT * FROM '+'#Table'+'';
-- SELECT #Temp;
EXEC [dbo].[sp_executesql]
#Temp
,N'#Table MyTable READONLY'
,#Table;