How can this be achieved in SQL???????

Question

Hi Guys,
This is my query:
SELECT  distinct iy.trial_no,
       iypa.amendment_no,
       iy.country_code,
       iy.country_desc,
       iypa.amend_reg_submission_date,
       iypa.amend_reg_approval_date,
       iypa.amend_reg_comments,
       iyea.ea_amendment_submission_date,
       IYEA.ea_amendment_approval_date,
       iyea.ea_amendment_expiry_date,
       iyea.ea_approval_comments,
    iyea.master_approval_flag      
FROM   irt_trc_protocol_amendment iypa,
       irt_trc_ethical_approvl_amend iyea,
       irt_trial_country iy
WHERE  iypa.trial_no = iyea.trial_no
AND    iypa.amendment_no = iyea.amendment_no
AND    iypa.country_code = iyea.country_code
AND    iypa.trial_no=101416
AND    iy.trial_no= iypa.trial_no
AND    iypa.country_code = 'GBR'
AND    iypa.country_code = iy.country_code 
AND    iyea.amendment_no = 4
AND    IYEA.master_approval_flag = 1 The above query will only ever return one row because only one record can have it's master_approval_flag set to 1. However multiple records can have a master_approval_flag set to 0.
This is what I want my query to acheive:
Select the one row where master_approval_flag = 1. If there is no record where master_approval_flag = 1, then still only display one row but ommit the details from the IYEA table and only include
the data from the IYPA table - Such that the output will only ever return one row....
How can I do this?
Thanks!

Answer 1

This should work:
select t.*
SELECT  distinct
       iy.trial_no,
       iypa.amendment_no,
       iy.country_code,
       iy.country_desc,
       iypa.amend_reg_submission_date,
       iypa.amend_reg_approval_date,
       iypa.amend_reg_comments,
       iyea.ea_amendment_submission_date,
       IYEA.ea_amendment_approval_date,
       iyea.ea_amendment_expiry_date,
       iyea.ea_approval_comments,
       iyea.master_approval_flag
      ,row_number() over (order by iyea.Master_Approval_Flag desc) rn
FROM   irt_trc_protocol_amendment     iypa,
       irt_trc_ethical_approvl_amend  iyea,
       irt_trial_country              iy
WHERE  iypa.trial_no                  = iyea.trial_no
AND    iypa.amendment_no              = iyea.amendment_no
AND    iypa.country_code              = iyea.country_code
AND    iypa.trial_no                  = 101416
AND    iy.trial_no                    = iypa.trial_no
AND    iypa.country_code              = 'GBR'
AND    iypa.country_code              = iy.country_code 
AND    iyea.amendment_no              = 4
) t
where rn = 1You could possibly remove the DISTINCT and specify
      ,row_number() over (order by iyea.Master_Approval_Flag desc, iy.Tria_No, iy.Amendment_No) rn
-- instead of
,row_number() over (order by iyea.Master_Approval_Flag desc) rnSince you are guranteed to always return a single row there may be no reason to use DISTINCT, which would probably slow the query down somewhat.