请问关于SQL视图的有关问题_Sql Server

请教关于SQL视图的问题
CREATE    view V_sk
as
select srbz,sflb,(case when sflb='AAAA' then 'AAAA' else sfxm end) as sfxm,skrq,jkfs,ysbh,ysxm,sksbh,sksm,zxksbh,zxksm,jzksbh,jzksm,sfdm,mc,dw,gg,jx,sl,
       zyfs,zl,lsj,lsje,skyjzrq,ksjzrq,cfysje,cfssje,cfbz,fjf from y_sk left join
      v_mzsfxm on y_sk.sfdm=v_mzsfxm.xmdm

在这个SQL语句建立的视图中，如何使sfxm为 null 的记录的sfxm字段的值换成sflb字段的值，多谢！
------解决思路----------------------

CREATE    view V_sk
as
select srbz,sflb,(case when sflb='AAAA' then 'AAAA' WHEN sfxm IS NULL THEN sflb else sfxm end) as sfxm,skrq,jkfs,ysbh,ysxm,sksbh,sksm,zxksbh,zxksm,jzksbh,jzksm,sfdm,mc,dw,gg,jx,sl,
       zyfs,zl,lsj,lsje,skyjzrq,ksjzrq,cfysje,cfssje,cfbz,fjf from y_sk left join
      v_mzsfxm on y_sk.sfdm=v_mzsfxm.xmdm

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