Temporary tables are dependent of Transactions. They behave like ordinary tables when they are placed in a transaction. Rollback and Commit transactions affect the data in Table variables.

[sql]
SET NOCOUNT ON
IF OBJECT_ID(‘tempdb.dbo.#TempTable1’) IS NOT NULL
DROP TABLE #TempTable1

DECLARE @TableVariable1 TABLE (VALUE VARCHAR(50))
CREATE TABLE #TempTable1 (VALUE VARCHAR(50))

INSERT INTO @TableVariable1(VALUE)
SELECT ‘INSERTED AFTER CREATION’

INSERT INTO #TempTable1(VALUE)
SELECT ‘INSERTED AFTER CREATION’

BEGIN TRAN

INSERT INTO @TableVariable1(VALUE)
SELECT ‘INSERTED IN TRANSACTION’

INSERT INTO #TempTable1(VALUE)
SELECT ‘INSERTED IN TRANSACTION’

DECLARE @TableVariable2 TABLE (VALUE VARCHAR(50))

CREATE TABLE #TempTable2 (VALUE VARCHAR(50))

INSERT INTO @TableVariable2(VALUE)
SELECT ‘INSERTED AFTER CREATION’

INSERT INTO #TempTable2(VALUE)
SELECT ‘INSERTED AFTER CREATION’

DROP TABLE #TempTable1

ROLLBACK TRAN

SELECT ‘@TableVariable1’ AS TableName,* FROM @TableVariable1
SELECT ‘#TempTable1’ AS TableName,* FROM #TempTable1
SELECT ‘@TableVariable2’ AS TableName,* FROM @TableVariable2
SELECT ‘#TempTable2’ AS TableName,* FROM #TempTable2
[/sql]

Output:

TableName       VALUE
--------------- --------------------------------------------------
@TableVariable1 INSERTED AFTER CREATION
@TableVariable1 INSERTED IN TRANSACTION

TableName   VALUE
----------- --------------------------------------------------
#TempTable1 INSERTED AFTER CREATION

TableName       VALUE
--------------- --------------------------------------------------
@TableVariable2 INSERTED AFTER CREATION


Msg 208, Level 16, State 0, Line 37
Invalid object name '#TempTable2'.

From the above output we can come up with the following notes:

• Data in the temporary tables is directly bound to transactions
  i.e. If the transaction is rolledback then the data inserted/Modified in the transaction is lost
• Data in the table variables is not bound to transactions.
  i.e. If the transaction is rolledback then the data inserted/Modified in the transaction is not lost.
• Creation/Deletion of temp tables is also bound to transactions.
  i.e. Temporary tables created in a transaction does not exist further if the transaction is rolled back, Temporary tables dropped in a transaction exist further if the transaction is rolled back.
• If a Table variable is created in a transaction it exists further even if the transaction is rolled back.

RETURN 1
END
[/sql]
Executes succesfully.

[sql]
CREATE FUNCTION dbo.TestFn( @i int)
RETURNS INT
AS
BEGIN
CREATE TABLE #A( I INT)

RETURN 1
END
[/sql]
Fails with an error:

Msg 2772, Level 16, State 1, Procedure TestFn, Line 5
Cannot access temporary tables from within a function.

Table variables should be referenced with an alias when used in joins etc where as alias is not mandatory for Table Variables

[sql]
CREATE TABLE #Values1 (ID INT,VALUE VARCHAR(100))
CREATE TABLE #Values2 (ID INT,VALUE VARCHAR(100))

INSERT INTO #Values1 (ID, VALUE)
SELECT 1,’A’
UNION
SELECT 2,’B’

INSERT INTO #Values2 (ID, VALUE)
SELECT 1,’A’
UNION
SELECT 3,’C’

SELECT * FROM #Values1 JOIN #Values2
ON #Values1.ID = #Values2.ID
[/sql]
Executes Successfully!!

[sql]
DECLARE @Values1 TABLE (ID INT,VALUE VARCHAR(100))
DECLARE @Values2 TABLE (ID INT,VALUE VARCHAR(100))

INSERT INTO @Values1 (ID, VALUE)
SELECT 1,’A’
UNION
SELECT 2,’B’

INSERT INTO @Values2 (ID, VALUE)
SELECT 1,’A’
UNION
SELECT 3,’C’

SELECT * FROM @Values1 JOIN @Values2
ON @Values1.ID = @Values2.ID
[/sql]
Fails with an error:

Msg 137, Level 16, State 1, Line 15
Must declare the scalar variable “@Values1”.
Msg 137, Level 16, State 1, Line 15
Must declare the scalar variable “@Values2”.

Temporary tables can be dropped explicitly where as dropping table variables is not possible
[sql]
DECLARE @TableVaraiabe TABLE (ID INT,VALUE VARCHAR(100))
DROP TABLE @TableVaraiabe
[/sql]
Fails with error:

Msg 102, Level 15, State 1, Line 2
Incorrect syntax near ‘@TableVaraiabe’.

[sql]
CREATE TABLE #TableVaraiabe (ID INT,VALUE VARCHAR(100))
DROP TABLE #TableVaraiabe
[/sql]
Executes Successfully!!

DDL Statements can be applied on temporary tables to add/modify and delete the columns but table variables cannot be altered after they are declaration.
[sql]
SET NOCOUNT ON
IF OBJECT_ID(‘tempdb.dbo.#TempTable1’) IS NOT NULL
DROP TABLE #TempTable1

CREATE TABLE #TempTable1 (VALUE VARCHAR(50))
ALTER TABLE #TempTable1 ADD VALUE1 VARCHAR(50)
[/sql]
Executes Successfully!!

[sql]
DECLARE @TableVariable1 TABLE (VALUE VARCHAR(50))
ALTER TABLE @TableVariable1 ADD VALUE1 VARCHAR(50)
[/sql]
Gives Error!!

Temporary Tables can be truncated where as table variables cannot.

[sql]
DECLARE @TableVaraiabe TABLE (ID INT,VALUE VARCHAR(100));
SELECT * FROM @TableVaraiabe
GO
SELECT * FROM @TableVaraiabe
[/sql]
The statement after go fails as the table variables scope ends with the first batch.
Error:

Msg 1087, Level 15, State 2, Line 1
Must declare the table variable “@TableVaraiabe”.

In nested procedures temporary tables are visible to the procedures called where as table variables are not.
[sql]
CREATE TABLE #Values1 (ID INT,VALUE VARCHAR(100))

INSERT INTO #Values1 (ID, VALUE)
SELECT 1,’A’
UNION
SELECT 2,’B’

EXEC sp_executesql @statement = N’SELECT * FROM #Values1′
[/sql]
Executes Successfully!!
[sql]
DECLARE @Values1 TABLE (ID INT,VALUE VARCHAR(100))

INSERT INTO @Values1 (ID, VALUE)
SELECT 1,’A’
UNION
SELECT 2,’B’

EXEC sp_executesql @statement = N’SELECT * FROM @Values1′
[/sql]
Fails as the table variable @Values1 is not visible to sp_executesql Procedure.
Error:

Msg 1087, Level 15, State 2, Line 1
Must declare the table variable “@Values1”.

Temporary tables are created in the same way similar to creating permanent tables.
[sql]
DECLARE @TableVaraiabe TABLE (ID INT,VALUE VARCHAR(100))
[/sql]

Temporary tables can be created using SELECT * INTO clause where as its not possible for Table variables.
[sql]
SELECT * INTO #TempTable FROM (
SELECT 1 AS I) AS A
[/sql]
Executes Successfully!!

[sql]
SELECT * INTO @TempTable FROM (
SELECT 1 AS I) AS A
[/sql]
Fails with the error:

Msg 102, Level 15, State 1, Line 1
Incorrect syntax near ‘@TempTable’.
Msg 156, Level 15, State 1, Line 2
Incorrect syntax near the keyword ‘AS’.