求各位大神帮我看下这条SQL？

[u010494052]

select sys_guid() AS LCID,
       (select yhmc from NX_UserInfo where yhbm = a.add_user and rownum < 2) as CJRMC,--这条select语句yhmc字段可能查出来是null，如果为null的话就取a.add_user,请问这里怎么修改？
       (select jgbm from pmsadm.yzx_jgdyxx@sc_link where gisjgbm = (select jgmc from NX_UserInfo where yhbm = a.add_user and rownum < 2)) AS CJDW,
       to_number(to_char(a.ADD_DATE,'yyyymmdd')) AS CJRQ,
       '0' AS YXYWBH,
       '0' AS SCYWBH,
       to_char(a.TASK_ID) AS DDYWBH,
       case a.task_source when 1 then '配网工程电子化移交流程' 
       when 2 then '基建及大修技改电子化移交流程' 
       when 5 then '基建及大修技改电子化移交流程'  end as LCMC,
       case a.TASK_STATUS when '-2' then 1 
       when '1' then 2 
       else 0 end as LCZT,
       a.MAINTAIN_CONTENT AS YJDSM,
       (select yjbdzsl from ext_scdy_yjsl where task_id = a.task_id) as YJBDZSL,
       (select yjxlsl from ext_scdy_yjsl where task_id = a.task_id) as YJXLSL,
       (select yjbyqsl from ext_scdy_yjsl where task_id = a.task_id) as YJBYQSL,
       0 AS YJYHSL,
       0 AS YJBJSL,
       to_char(a.ADD_DATE,'yyyymmdd') AS FQZJ,
       a.add_user as CJRBH,
       (select bmmc from NX_UserInfo where yhbm = a.add_user and rownum < 2) as CJBM,
       to_number(to_char(a.ADD_DATE,'hhmmss')) AS CJSJ,
       a.task_type AS TASK_TYPE 
from txwh_feature_mt_app a 

查询出来的结果CJRMC会有空值如下图：

[immmmmmmm]

nvl((select yhmc from NX_UserInfo where yhbm = a.add_user and rownum < 2) ,a.add_user) CJRMC

[u010494052]

引用 1 楼 tianmingt 的回复:

nvl((select yhmc from NX_UserInfo where yhbm = a.add_user and rownum < 2) ,a.add_user) CJRMC

忘了这个缕空函数了，谢谢大神！