How do I get the value associated with a MIN or MAX - sql

Question

I'm in the middle of creating a query and have it where I need the other values, however I am pulling a MIN and MAX date for individual patient_id. I'm wondering how I would go about how I would pull a value associated with that MIN or MAX date as well? I'm looking for a value the column provider_id which will show which doctor they saw on that MIN or MAX date. Here is what I have so far:
WITH test AS (
SELECT patient_id,
clinic,
SUM(amount) AS production,
MIN(tran_date) AS first_visit,
MAX(tran_date) AS last_visit
FROM transactions
WHERE impacts='P'
GROUP BY patient_id, clinic)
SELECT w.patient_id,
w.clinic,
p.city,
p.state,
p.zipcode,
p.sex,
w.production,
w.first_visit,
w.last_visit
FROM test w
LEFT JOIN patient p
ON (w.patient_id=p.patient_id AND w.clinic=p.clinic)

Answer 1

I believe that this will get what you're looking for:
;WITH CTE_Transactions AS (
SELECT DISTINCT
patient_id,
clinic,
SUM(amount) OVER (PARTITION BY patient_id, clinic) AS production,
FIRST_VALUE(tran_date) OVER (PARTITION BY patient_id, clinic ORDER BY tran_date) AS first_visit,
FIRST_VALUE(provider_id) OVER (PARTITION BY patient_id, clinic ORDER BY tran_date) AS first_provider_id,
LAST_VALUE(tran_date) OVER (PARTITION BY patient_id, clinic ORDER BY tran_date) AS last_visit,
LAST_VALUE(provider_id) OVER (PARTITION BY patient_id, clinic ORDER BY tran_date) AS last_provider_id,
ROW_NUMBER() OVER (PARTITION BY patient_id, clinic ORDER BY tran_date) AS row_num
FROM Transactions
WHERE impacts='P'
)
SELECT
w.patient_id,
w.clinic,
p.city,
p.state,
p.zipcode,
p.sex,
w.production,
w.first_visit,
w.last_visit
FROM
CTE_Transactions W
LEFT JOIN Patient P ON
W.patient_id = P.patient_id AND
W.clinic = P.clinic
INNER JOIN Provider FIRST_PROV ON
FIRST_PROV.provider_id = W.first_provider_id
INNER JOIN Provider LAST_PROV ON
LAST_PROV.provider_id = W.last_provider_id
WHERE
W.row_num = 1

Answer 2

I assume you are referring to the CTE. You can use conditional aggregation along with window functions. For instance, to get the amount for the first visit:
WITH test AS (
SELECT patient_id, clinic,
SUM(amount) AS production,
MIN(tran_date) AS first_visit,
MAX(tran_date) AS last_visit,
SUM(CASE WHEN tran_date = min_tran_date THEN amount END) as first_amount
FROM (SELECT t.*,
MIN(trans_date) OVER (PARTITION BY patient_id, clinic) as min_tran_date
FROM transactions
WHERE impacts = 'P'
) t
GROUP BY patient_id, clinic
)