Sub query not executing

Question

i am running these SQL lines but getting error but this DISCH_SUM_ID is there in my table
disch_sum_hdr
select disch_sum_hdr.*,
SELECT CASE NVL(Disch_sum_Dtl.Disch_Res_Col_1,0) WHEN 1 THEN 'DEATH SUMMARY'
ELSE 'DISCHARGE SUMMARY' END As DiscSummTitle
from Disch_sum_Dtl
LEFT JOIN Disch_sum_Dtl Disch_sum_Dtl_1
ON Disch_sum_Dtl_1.DISCH_SUM_ID = Disch_sum_Hdr.DISCH_SUM_ID
) as DiscTitle
from disch_sum_hdr
Error
ORA-00904: "DISCH_SUM_HDR"."DISCH_SUM_ID": invalid identifier
00904. 00000 - "%s: invalid identifier"
*Cause:   
*Action:
Error at Line: 7 Column: 45

Answer 1

Like Sylvie, I'm not sure what you are trying to do, but I think what you are looking for is more like:
select disch_sum_hdr.*,
       (SELECT CASE NVL(Disch_sum_Dtl.Disch_Res_Col_1,0) WHEN 1 THEN 'DEATH SUMMARY'
                  ELSE 'DISCHARGE SUMMARY' END As DiscSummTitle
        from Disch_sum_Dtl
        where Disch_sum_Dtl.DISCH_SUM_ID = Disch_sum_Hdr.DISCH_SUM_ID) as DiscTitle
from disch_sum_hdrYou do not need a join in the scalar sub-query here. If that is what you want, then I would be inclined to write it as a straight outer join like:
select disch_sum_hdr.*,
       CASE NVL(Disch_sum_Dtl.Disch_Res_Col_1,0)
          WHEN 1 THEN 'DEATH SUMMARY'
          ELSE 'DISCHARGE SUMMARY' END As DiscTitle
from disch_sum_hdr
   left join Disch_sum_Dtl
      on Disch_sum_Dtl.DISCH_SUM_ID = Disch_sum_Hdr.DISCH_SUM_IDwhich is likely to be more efficient.
John