T-SQL Select all from TableA and condition on TableB
TableA Columns: A_ID, NAME, SOURCE, TITLE, EVENTID
TableB Columns: B_ID, EVENTID, CODE, FIELD

TableA                                 |   TableB
-----------------------------------------------------------------------
A_ID, NAME, SOURCE, TITLE, EVENTID     |   B_ID, EVENTID, CODE, FIELD
-----------------------------------------------------------------------
1     john  s1      x      100         |   1     100      5     textA
2     bruce s2      y      105         |   2     100      10    textB
3     bob   s3      z      110         |   3     105      5     textC
                                       |   4     110      5     textD
                                       |   5     110      10    textE

[ john  | s1 | x | textB ]
[ bruce | s2 | y |       ]
[ bob   | s3 | z | textE ]

SELECT A.NAME,
       A.SOURCE,
       A.TITLE,
       B.FIELD
FROM   TableA A
       LEFT JOIN TableB B
         ON A.EVENTID = B.EVENTID
            AND B.CODE = 10

SELECT a.NAME, a.SOURCE, a.TITLE, b.FIELD
  FROM TableA a
       LEFT JOIN TableB b ON b.EventId = a.EventId
             AND b.Code = 10