MYSQL calculating an average on a count

问题

I have a simple query that I want an average on. This is what it looks like now, and I want to know the average of my count per Opname_OpnameID.

SELECT Opname_OpnameID, count(*) as 'behandelingen per opname'
FROM behandeling
GROUP BY Opname_OpnameID

回答1:

If you want the average count, presumably over the entire table, then just do exactly that:

SELECT AVG(cnt) AS total_avg
FROM ( 
    SELECT COUNT(*) AS cnt FROM behandeling GROUP BY Opname_OpnameID
) t;

回答2:

You can use count(distinct) and not use a subquery:

SELECT count(*) / count(distinct Opname_OpnameID)
FROM behandeling

来源：https://stackoverflow.com/questions/50332526/mysql-calculating-an-average-on-a-count