How can I group by sub query like main query?

August 22, 2024

How can I apply group by subquery like main query ?

This is the query :

select a.clinic_no , 
b.CLINIC_DESC_A , 
a.doctor_no , 
c.STAFF_NATIVE_NAME , 
count(DISCHARGE_FROM_CLINIC) , 
(select count(patient_no) from trng.opd_visits_history WHERE event_date BETWEEN 20240815 and 20240822) as "Total"
from trng.opd_visits_history a , trng.hospital_clinics b  , trng.hospital_staff c 
WHERE event_date BETWEEN 20240815 and 20240822
 and a.CLINIC_NO = b.CLINIC_NO
and a.DOCTOR_NO = c.STAFF_NO 
and b.DOCTOR_NO = c.STAFF_NO
and a.HOSPITAL_NO = 720022
and b.HOSPITAL_NO = 720022
and c.HOSPITAL_NO = 720022  
AND a.DISCHARGE_FROM_CLINIC = 1
group by a.clinic_no , a.doctor_no , b.CLINIC_DESC_A , c.STAFF_NATIVE_NAME

The output like this :

clinic no       doctor no            discharge from clinic    total 
   10               22                         5                1230
   12               15                         4                1230 
   16               19                         7                1230
   20               13                         2                1230

I need to group by subquery like this :

select count(patient_no) from trng.opd_visits_history WHERE event_date BETWEEN 20240815 and 20240822 group by clinic_no , doctor_no

when I use group by inside with subquery it show error

ORA-01427 single row subquery returns more than one row

>Solution :

You’re trying to use a correlated subquery, but – you didn’t apply any correlation between its table to outside table(s). It must return only one row (value), but – when you put group by clause into it – it caused more than a single row to be returned and you got an error.

Something like this might do (I also JOINed tables on common columns and let WHERE clause to filter resulting rows):

  SELECT a.clinic_no,
         b.clinic_desc_a,
         a.doctor_no,
         c.staff_native_name,
         COUNT (discharge_from_clinic),
         (SELECT COUNT (patient_no)
            FROM trng.opd_visits_history h
           WHERE     h.clinic_no = a.clinic_no                            --> this
                 AND h.doctor_no = a.doctor_no                            --> this
                 AND event_date BETWEEN 20240815 AND 20240822) AS "Total"
    FROM trng.opd_visits_history a
         JOIN trng.hospital_clinics b
            ON     a.clinic_no = b.clinic_no
               AND a.hospital_no = b.hospital_no
         JOIN trng.hospital_staff c
            ON     a.doctor_no = c.staff_no
               AND b.doctor_no = c.staff_no
               AND c.hospital_no = a.hospital_no
   WHERE     event_date BETWEEN 20240815 AND 20240822
         AND a.hospital_no = 720022
         AND a.discharge_from_clinic = 1
GROUP BY a.clinic_no,
         a.doctor_no,
         b.clinic_desc_a,
         c.staff_native_name