I need to pull unique patients that meet certain criteria - sql

Question

I pulled person_nbrs that have never had an EventType1 before or after an EventType2. I need to pull person_nbrs that have not had an EventType1 prior to having an EventType2. If they had an EventType1 after an EventType2, than it is to be ignored. Here is my query that pulls person_nbrs that have never had an EventType1 before or after EventType2.
SELECT
person_nbr, enc_nbr, enc_timestamp
FROM
person p
JOIN
patient_encounter pe ON p.person_id = pe.person_id
JOIN
patient_procedure pp ON pe.enc_id = pp.enc_id
WHERE
enc_timestamp >= '20170101'
--EventType2
AND code_id LIKE '2'
-- EventType1
AND person_nbr NOT IN (SELECT person_nbr
FROM person p
JOIN patient_encounter pe ON p.person_id = pe.person_id
JOIN patient_procedure pp ON pe.enc_id = pp.enc_id
WHERE code_id LIKE '1')
GROUP BY
person_nbr, enc_nbr, enc_timestamp
ORDER BY
person_nbr ;

Answer 1

You can do this with aggregation and a HAVING clause:
SELECT p.person_nbr
FROM person p JOIN
patient_encounter pe
ON p.person_id = pe.person_id JOIN
patient_procedure pp
ON pe.enc_id = pp.enc_id
GROUP BY p.person_nbr
HAVING SUM(CASE WHEN pp.code_id = 2 THEN 1 ELSE 0 END) > 0 AND -- has code 2
(MAX(CASE WHEN pp.code_id = 1 THEN pe.timestamp END) IS NULL OR
MAX(CASE WHEN pp.code_id = 1 THEN pe.timestamp END) < MIN(CASE WHEN pp.code_id = 2 THEN pe.timestamp END)
) ;
The HAVING clause has two parts:
The first specifies that the person has a code = 2.
The second specifies one of two conditions. The first is that there is no code = 1. The second alternative is that the latest c = 1 timestamp is less than the earliest code = 2 timestamp.