UPDATE TAB_A t1
 SET (V_TILL) = (SELECT TO_DATE(t2.D_DATE,'YYYYMMDD')
                       FROM B t2
                      WHERE t1.BR_CODE = t2.BR_CODE
                      AND t1.BK_CODE = t2.BK_CODE||t2.BR_CODE)
WHERE EXISTS (
  SELECT 1
    FROM TAB_B t2
   WHERE t1.BR_CODE = t2.BR_CODE
   AND t1.BK_CODE = t2.BK_CODE||t2.BR_CODE)

SET (V_TILL) = (SELECT TO_DATE(t2.D_DATE,'YYYYMMDD')
                       FROM B t2
                      WHERE t1.BR_CODE = t2.BR_CODE
                      AND t1.BK_CODE = t2.BK_CODE||t2.BR_CODE AND ROWNUM <=1)

SET (V_TILL) = (SELECT DISTINCT TO_DATE(t2.D_DATE,'YYYYMMDD')
                       FROM B t2
                      WHERE t1.BR_CODE = t2.BR_CODE
                      AND t1.BK_CODE = t2.BK_CODE||t2.BR_CODE)

MERGE INTO TAB_A A
USING TAB_B B
ON (A.BK_CODE = B.BK_CODE || B.BR_CODE
AND A.BR_CODE = B.BR_CODE AND B.BR_DISP_TYPE <> '0'
AND ((B.BK_CODE, B.BR_SUFFIX) IN (SELECT BK_CODE,
                                        MIN(BR_SUFFIX)
                                        FROM TAB_B
                                        GROUP BY BK_CODE)))