SELECT tableA.Id, tableB.Id FROM tableA JOIN tableB ON (tableA.bId = tableB.Id)

while($result = mysql_fetch_array(mysql_query(/Query Above/)){
    print $result['tableB.Id'];
}

SELECT tableA.Id AS aId, tableB.Id AS bId
FROM tableA
JOIN tableB ON (tableA.bId = tableB.Id)

SELECT tableA.*, tableB.* FROM tableA JOIN tableB ON (tableA.bId = tableB.Id)