I'm not sure what you want to achieve, but see below example:
DECLARE @tab1 TABLE (AID INT IDENTITY(1,1), aDescription VARCHAR(30))
INSERT INTO @tab1 (aDescription)
SELECT 'ABC'
UNION ALL SELECT 'DEF'
UNION ALL SELECT 'GHI'
UNION ALL SELECT 'JKL'
DECLARE @tab2 TABLE (BID INT IDENTITY(1,1), AIDReference INT)
INSERT INTO @tab2 (AIDReference)
SELECT 1
UNION ALL SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 2
UNION ALL SELECT 6
UNION ALL SELECT 2
SELECT a.AID, b.BID, a.aDescription
FROM @tab1 AS a INNER JOIN @tab2 AS b ON a.AID = b.AIDReference
Result:
1 1 ABC
1 2 ABC
2 3 DEF
2 4 DEF
2 6 DEF
For furhter information, please, see:
Visual Representation of SQL Joins[
^]
[EDIT]
If you want to enumerate all BIDs for each AID in one row, please, see this:
SELECT a.AID, a.aDescription, STUFF( (SELECT',' + CONVERT(VARCHAR(30), b.BID) AS 'text()'
FROM @tab2 AS b
WHERE a.AID = b.AIDReference
FOR XML PATH('')), 1, 1, '') AS [BIDs]
FROM @tab1 AS a
GROUP BY a.AID, a.aDescription
Result:
AID Desc.. BIDs
1 ABC 1,2
2 DEF 3,4,6
3 GHI NULL
4 JKL NULL
[/EDIT]