Question

I have a users table, and an appointments table. For any given day, I would like a query that selects

1) the user_id the appointment is scheduled with

2) the number of appointments for that user for the specified day.

It seems I can one or the other, but I’m unsure of how to do it with one query. For instance, I can do:

SELECT user_id FROM appt_tbl WHERE DATE(appt_date_time) = '2012-10-14' 
group by user_id;

Which will give me the users that have an appointment that day, but how can I add to this query another column that will give me how many appointments each user has? Assuming I need some kind of subquery, but I’m unsure of how to structure that.

Answer 1

SQL uses the notion of “aggregate functions” to get you this information. You can use them with any aggregating query (i.e. it has “group by” in it).

SELECT user_id, count(*) as num_apts ...