带有 WHERE EXISTS 的 SQL UPDATE 语句

Question

我正在尝试编写一个查询，仅当我更新的组的 LINE_CD 为 50 时才更新日期。我会这样做吗？

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
  );

但是，如果您可以从查询中获取此信息，为什么还要更新表呢？看来这必须不断运行，否则就有过时的风险。