Question

I have following tables in my MySql database :

+----------------------------------------------+
                      PROJECT
+----------------------------------------------|
+----------------------------------------------|
  project_id | team_size | from_date
+----------------------------------------------|
    1        |   34      |  1 Dec 2010
+----------------------------------------------|
    2        | 2         | 2 Jan 1902
+----------------------------------------------|
    3        | 99        | 15 Aug 1947
+----------------------------------------------+

---

+----------------------------------------------+
        Technologies
+----------------------------------------------+
+----------------------------------------------+
 technology_id | technology_name
+----------------------------------------------+
       1       | Java
+----------------------------------------------+
       2       | CPP
+----------------------------------------------+
       3       | Hibernate
+----------------------------------------------+
       4       | EJB
+----------------------------------------------+
       5       | Python
+----------------------------------------------+
       6       | Hadoop
+----------------------------------------------+
       7424    | Perl
+----------------------------------------------+

---

To link Project and Technologies tables I have following table :

+----------------------------------------------+
        Project_Technologies
+----------------------------------------------+
+----------------------------------------------+
   Project_ID   | Technology_ID
+----------------------------------------------+
    1           | 2
+----------------------------------------------+
    1           | 7424
+----------------------------------------------+
    2           | 1
+----------------------------------------------+
    2           | 3
+----------------------------------------------+
    2           | 4
+----------------------------------------------+
    2           | 5
+----------------------------------------------+

I want to show data in one table in the form of rows and columns in UI.
For example :

+---------------------------------------------------+
  project_id | team_size | from_date | technologies 
|---------------------------------------------------|
|     1      |   34      | 1 Dec 2010| CPP, Perl    |
|---------------------------------------------------|
|     2      |   2       | 2 Jan 1902| Java, Hibernate, EJB, Python |
|---------------------------------------------------|
|     3      |   99      |15 Aug 1947|              |
+---------------------------------------------------+

I am not able to form sql query to get something like this. I have tried following query which is giving me duplicate rows.

select pr.project_id,pr.team_size,pr.from_date,tech.technology_name
from project pr, project_technologies ptech, technologies tl
where pr.project_id=ptech.project_id and ptech.technology_id=tl.technology_id

I would like to know how to avoid duplicate rows? Currently this query is giving me 2 rows when project_id=1 and 4 rows when project_id=2

Answer 1

This should do the trick… a group by and a group_concat

select 
    pr.project_id, 
    pr.team_size, 
    pr.from_date, 
    GROUP_CONCAT(tech.technology_name separator ', ') as technologies
from  
    project pr 
    JOIN project_technologies ptech ON pr.project_id=ptech.project_id
    JOIN technologies tl ON ptech.technology_id=tl.technology_id
GROUP BY
    pr.project_id, 
    pr.team_size, 
    pr.from_date

EDIT fixed to include JOIN clause