Use of Table variable in SQL Server

Hi Team,
I am using SQL Server 2005. I have heard that we can use a table variable to use instead of LEFT OUTER JOIN.
What I understand is that, we have to put all the values from the left table to the table variable, first. Then we have to UPDATE the table variable with the right table values. Then select from the table variable.
Has anyone come across this kind of approach? Could you please suggest a real time example (with query)?
I have not written any query for this. My question is - if someone has used a similar approach, I would like to know the scenario and how it is handled. I understand that in some cases it may be slower than the LEFT OUTER JOIN.
Please assume that we are dealing with tables that have less than 5000 records.
Thanks

I am trying to learn optimization in SQL. Following queries explains my thoughts. Both of them took 19 seconds.
Is there any scenario in which the second approach will perform better? Introduction if indexes/ more data in either of the tables / more complex calculations - anything?CREATE TABLE #MainTable ( CustomerID
INT PRIMARY KEY, FirstName
VARCHAR(100) ) DECLARE @Count INT
SET
@Count = 0DECLARE @Iterator INT
SET
@Iterator = 0WHILE
@Count <8000BEGIN
INSERT INTO #MainTable SELECT @Count, 'Cust'+CONVERT(VARCHAR(10),@Count)
SET @Count = @Count+1ENDCREATE
TABLE #RightTable ( OrderID
INT PRIMARY KEY, CustomerID INT, Product
VARCHAR(100) ) CREATE
INDEX [IDX_CustomerID] ON #RightTable (CustomerID)WHILE
@Iterator <400000BEGINIF @Iterator % 2 = 0
BEGIN
INSERT INTO #RightTable SELECT @Iterator,2, 'Prod'+CONVERT(VARCHAR(10),@Iterator)
END
ELSE
BEGIN
INSERT INTO #RightTable SELECT @Iterator,1, 'Prod'+CONVERT(VARCHAR(10),@Iterator)END
SET
@Iterator = @Iterator+1END-- Approach 1: Using LEFT JOINSELECT
mt.CustomerID,mt.FirstName,COUNT(rt.Product) [CountResult]FROM #MainTable mt
LEFT JOIN #RightTable rt ON mt.CustomerID = rt.CustomerID GROUP BY mt.CustomerID,mt.FirstName ---------------------------
-- Approach 2: Using Table variable UpdateDECLARE
@WorkingTableVariable TABLE( CustomerID
INT, FirstName
VARCHAR(100),ProductCount
INT ) INSERT
INTO @WorkingTableVariable (CustomerID,FirstName)SELECT CustomerID, FirstName FROM #MainTable UPDATE
@WorkingTableVariable SET
ProductCount = [Count]FROM @WorkingTableVariable wt
INNER JOIN(SELECT CustomerID,COUNT(rt.Product) AS [Count]
FROM #RightTable rtGROUP BY CustomerID) IV ON wt.CustomerID = IV.CustomerID SELECT
CustomerID,FirstName, ISNULL(ProductCount,0) [CountResult] FROM @WorkingTableVariable ORDER
BY CustomerID--------DROP
TABLE #MainTableDROP
TABLE #RightTable

Thanks for your kind support