Question

Find Top 5 in table ?

Asked by: edvinson

I need to find the top 5 rated installers. Rating system is 1 to 5.




Installers Table:

+------------------------------+--------------+------+-----+---------+----------------+
| Field                        | Type         | Null | Key | Default | Extra
      |
+------------------------------+--------------+------+-----+---------+----------------+
| installer_id                 | int(11)      |      | PRI | NULL    | auto_increment |
| installer_first_name    | varchar(255) |      |     |         |                |
+------------------------------+--------------+------+-----+---------+----------------+


Ratings Table:


+--------------+---------+------+-----+---------+----------------+
| Field        | Type      | Null | Key | Default | Extra          |
+--------------+---------+------+-----+---------+----------------+
| ratings_id   | int(11)  |      | PRI | NULL    | auto_increment |
| installer_id  | int(11) |      |     | 0            |                |
| rating         | int(11) |      |     | 0             |                |
+--------------+---------+------+-----+---------+----------------+


Sample Data from Ratings:

+------------+--------------+--------+
| ratings_id | installer_id | rating |
+------------+--------------+--------+
|          1 |            1 |      3 |
|          2 |            1 |      4 |
|          3 |            2 |      5 |
|          4 |            2 |      3 |
|          5 |            3 |      2 |
|          6 |            3 |      5 |
|          7 |            4 |      3 |
|          8 |            4 |      1 |
+------------+--------------+--------+


So basically I want to see which 5 are the top rated installers.


Thank you.

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Asked On
2006-09-10 at 19:38:53ID21984367
Tags

top

,

5

Topic

MySQL Server

Participating Experts
2
Points
500
Comments
9

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Answers

 

by: sajuksPosted on 2006-09-10 at 19:44:52ID: 17491458

use the limit keyword

select installer_first_name  ,rating
 from Installers , Ratings
where Installers.installer_id  = Ratings.installer_id  
Order by rating desc limit 5

 

by: edvinsonPosted on 2006-09-10 at 19:48:48ID: 17491476

Don't you need to get the average rating first?

 

by: sajuksPosted on 2006-09-10 at 19:54:26ID: 17491494

select installer_first_name  ,avg(rating) as Rating
 from Installers , Ratings
where Installers.installer_id  = Ratings.installer_id  
group by installer_first_name  
Order by rating desc  limit 5

 

by: racekPosted on 2006-09-10 at 22:39:36ID: 17491931

Installers without rating included :

select installer_first_name  ,avg(rating) as Rating
   from Installers LEFT JOIN Ratings USING(installer_id )
   group by installer_first_name  
    Order by rating desc  limit 5

 

by: edvinsonPosted on 2006-09-11 at 05:10:42ID: 17493755

Perfect. Thanks to both. Yes, I also needed one with no rating.

 

by: edvinsonPosted on 2006-09-11 at 05:12:14ID: 17493765

Ps. Why group by installer_first_name   ?

 

by: racekPosted on 2006-09-11 at 05:16:28ID: 17493794

beacause you have AVG. You must have GROUP BY allways when you have aggregate functions (count, sum, avg etc)

 

by: edvinsonPosted on 2006-09-11 at 06:17:26ID: 17494190

but since we are using a JOIN as a condition, it really does nothing, is that correct?

 

by: racekPosted on 2006-09-11 at 06:57:42ID: 17494513

20120131-EE-VQP-002

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