我如何获取mysql中一列的总数？

Question

Alright, I am kind of new to SQL and I have no idea on how I am going to do this. I have tried to google but maybe I'm not sure if I am searching for the right question. So here it is. I have 2 tables in my database. One is called events and another one is called eventtypes .

My eventtype table looks like this..

-------------------
eventID | eventName|
   1    | eveA     |  
   2    | eveB     |  
   3    | eveC     |  
___________________

and my events table, looks like this

--------------------------
eventCat |UserRegistered |
   1     | John          |  
   2     | Mac           |  
   3     | Assz          | 
   2     | Ez            |  
   3     | Pz            |  
_________________________

(I hope you understand my table.....)

events.eventCat=eventtype.eventID

Now, what I am trying to do is to, calculate the numbers of participants for event 1, 2 and 3 in events table and later display the number of users who will be attending appropriately by using the eventtype table using php.

Can somebody help me out with this ? Thanks a bunch !

Answer 1

create table eventtype
(   eventID int not null,
    eventName varchar(100) not null
);
insert eventtype(eventID,eventName) values
(1,'eveA'),
(2,'eveB'),
(3,'eveC');

create table events
(   eventCat int not null,
    UserRegistered varchar(100) not null
);
insert events(eventCat,UserRegistered) values
(1,'John'),
(2,'Mac'),
(3,'Assz'),
(2,'Ez'),  
(3,'Pz');

Query:

select e.eventId,count(u.UserRegistered) as theCount 
from eventtype e 
join events u 
on u.eventCat=e.eventId 
group by e.eventId 
order by e.eventId; 
+---------+----------+
| eventId | theCount |
+---------+----------+
|       1 |        1 |
|       2 |        2 |
|       3 |        2 |
+---------+----------+

Answer 2

The followng query should work.it will select the no of participants based on the event using group by clause

 SELECT count(UserRegistered),eventName
 From events,eventype
 WHERE events.eventCat=eventtype.eventID
 GROUP BY eventCat

Answer 3

You can apply join and group by to acheive this -

SELECT count(UserRegistered),eventName from events join eventtype on
  events.eventCat=eventtype.eventID
     GROUP BY eventCat

Hope this will help you.