Oracle - Find Max and Least records from table - sql

Question

I have the following patients and appointments tables.
Patient
CREATE TABLE Patient
(
patientID number(10),
firstName varchar2(50) NOT NULL,
middleName varchar2(50),
surName varchar2(50) NOT NULL,
p_age number(10) NOT NULL,
p_gender char(1),
p_address varchar2(200),
p_contact_no number(10),
medicalHistory varchar2(500),
allergies varchar2(200),
CONSTRAINT PK_Patient PRIMARY KEY (patientID)
);
Appointment
CREATE TABLE Appointment
(
appID number(10),
patientId number(10),
staffId number(10),
appDateTime TIMESTAMP(3),
CONSTRAINT PK_Appointment PRIMARY KEY (appID),
CONSTRAINT FK_Appointment_Patient FOREIGN KEY (patientId) REFERENCES Patient(patientID) ON DELETE CASCADE,
CONSTRAINT FK_Appointment_Staff FOREIGN KEY (staffId) REFERENCES Staff(staffID) ON DELETE CASCADE
);
I want to get the patient details of patients having most and least appointments.
I have written the query in SQL server before and now I want to change it to oracle. Can anyone help me?
This is what I have so far.
SELECT p.patientId, p.firstName,
Count(a.appId) AS Count,
MAX(Count(a.appId)) OVER () AS MaxMyGroup,
MIN(Count(a.appId)) OVER () AS MinMyGroup
FROM Patient p INNER JOIN Appointment a ON p.patientID = a.patientId
GROUP BY p.patientId, p.firstName
SQL Query
WITH s
AS (SELECT p.patientId, p.firstName,
Count(a.appId) AS [Count],
MAX(Count(a.appId)) OVER () AS [MaxMyGroup],
MIN(Count(a.appId)) OVER () AS [MinMyGroup]
FROM Patient p INNER JOIN Appointment a ON p.patientID = a.patientId
GROUP BY p.patientId, p.firstName)
SELECT patientId AS ID,
firstName AS 'First Name',
V.[Count] AS 'Appointment Count',
Agg AS 'MAX/MIN'
FROM s
CROSS APPLY (VALUES ( 'Most', CASE WHEN [Count] = [MaxMyGroup] THEN [Count] END),
('Least', CASE WHEN [Count] = [MinMyGroup] THEN [Count] END))
V(Agg, [Count])
WHERE V.[Count] IS NOT NULL

Answer 1

You are almost there with your query - you just need to then filter on whether the number of appointments is equal to either the minimum or maximum number of appointments. (You also probably want to use LEFT OUTER JOIN rather than INNER JOIN.)
SELECT patientId,
firstName,
NumAppt,
CASE NumAppt
WHEN MinAppt
THEN 'Least'
ELSE 'Most'
END AS category
FROM (
SELECT p.patientId,
p.firstName,
Count(a.appId) AS NumAppt,
MAX(Count(a.appId)) OVER () AS MaxAppt,
MIN(Count(a.appId)) OVER () AS MinAppt
FROM Patient p
LEFT OUTER JOIN Appointment a
ON ( p.patientID = a.patientId )
GROUP BY p.patientId, p.firstName
)
WHERE NumAppt IN ( MinAppt, MaxAppt );

Answer 2

Check if this helps.
SELECT *
FROM PATIENT P
WHERE EXISTS
(SELECT PATIENTID,
COUNT(*)
FROM APPOINTMENT A
GROUP BY PATIENTID
HAVING P.PATIENTID = A.PATIENTID
AND (COUNT(*) >=
(SELECT MAX(COUNT(*)) FROM APPOINTMENT A2 GROUP BY A2.PATIENTID
)
OR COUNT(*) <=
(SELECT MIN(COUNT(*)) FROM APPOINTMENT A3 GROUP BY A3.PATIENTID
) )
)