SQL UPDATE statement with WHERE EXISTS

Question

Im trying to write a query that updates a date only if the group im updating has a LINE_CD of 50. Would i do it like this?

UPDATE EMPLOYER_ADDL  
SET EMPLOYER_ADDL.GTL_UW_APPRV_DT = EMPLOYER_ADDL.DNTL_UW_APPRV_DT 
WHERE EXISTS
    ( 
      SELECT EMP_PLAN_LINE_INFO.LINE_CD
      FROM EMP_PLAN_LINE_INFO
      Where EMP_PLAN_LINE_INFO.GR_NBR = EMPLOYER_ADDL.GR_NBR and
       EMP_PLAN_LINE_INFO.LINE_CD = 50
     )

Answer 1

UPDATE ea
  SET GTL_UW_APPRV_DT = DNTL_UW_APPRV_DT
  FROM EMPLOYER_ADDL AS ea
  WHERE EXISTS
  (
    SELECT 1
      FROM EMP_PLAN_LINE_INFO AS ep
      WHERE ep.GR_NBR = ea.GR_NBR
      AND ep.LINE_CD = 50
  );

However, if you can derive this information from a query, why update the table? Seems like this will have to be run constantly else risk being out of date.