SELECT RV.SIGN_CODE ,
IFNULL(RV.LAND_ID,'') as LAND_ID,
RV.SIGN_TYPE,
RV.SIGN_WIDE,
RV.SIGN_LONG,
IFNULL(RV.SIGN_AREA,'') as SIGN_AREA,
RV.SIGN_SIDE,
RV.SIGN_TEXT, (select RT.TITLE_NAME ,RT.FIRST_NAME,RT.LAST_NAME
from RV_TAX_PERSONAL RT
) as IDTRADE_NO
FROM RV_SIGN_MASTER RV,GLO_PROVINCE GP
ตรงตัวสีแดง มันขึ้นว่า "Operand should contain 1 column(S)"