Length of Stay by Provider

Let’s take a look at this request from a detailed and summary angle.

SELECT
   Lastname,
   firstname,
   id,
   COALESCE(provcode,'None') AS "Provider",
   Intakedate,dischargedate,
   DateDiff(day,intakedate,dischargedate) AS "Days"
FROM 
   sos.patients a
   JOIN sos.providers b ON a.providernum=b.providernum
WHERE
   intakedate IS NOT NULL
   and dischargedate IS NOT NULL

....will give you a list of patients, their intake and discharge dates, and the number of days between those
dates.

Extending that to give us a summary, with provider, average length of stay, and the number of patients
from which the statistics are derived:

SELECT
   COALESCE(provcode,'None') AS "Provider",
   COUNT(*) AS "N",
   AVG(DateDiff(day,intakedate,dischargedate)) AS "Days"
FROM 
   sos.patients a
   JOIN sos.providers b ON a.providernum=b.providernum
WHERE
   intakedate IS NOT NULL
   and dischargedate IS NOT NULL
GROUP BY 
   "Provider"
ORDER BY 
   "Provider"