MySQL: Combine multiple row values into single column? - mysql

Question

Database: MySQL
Table: Teams
TeamID INT
TeamName VARCHAR(20)
Table: People
PeopleID INT
FirstNameID INT
LastNameID INT
Table: TeamMembers
TeamID INT
PeopleID INT
Table Example: Teams
TeamID TeamName
1 Team Xstream
2 Team INsanity
Table Example: People
PeopleID FirstNameID LastNameID
1 1351 453
2 5463 763
3 976 8762
4 87 784
5 187 465
6 761 566
7 376 2134
Table Example: TeamMembers
TeamID PeopleID
1 1
1 3
1 7
2 2
2 4
2 5
2 6
Desired Output:
TeamName TeamMembers
Team Xstream John Smith/Jane Doe/Daniel Davis
Team INsanity Sally Sue/Tom Thomas/Jack Jones/Harry Henderson
There will not be a set number of TeamMembers per team, so it's not like I could have three subqueries because there will only be three team members. I've lightly looked online, but I always get the best and most thorough answers here. Any ideas or pointers, please let me know. I honestly have no idea where to begin here. Thanks.

Answer 1

I am guessing that the names of the people are actually stored somewhere considering you are just showing ID numbers as names. But you will want to use both CONCAT() and GROUP_CONCAT() for this result. The first step, will join all of the tables and use the CONCAT() function:
select t.teamname,
concat(p.FirstNameId, ' ', p.LastNameId) teamMembers
from teams t
left join teammembers m
on t.teamid = m.teamid
left join people p
on m.peopleid = p.peopleid;
See SQL Fiddle with Demo, which will produce the result:
| TEAMNAME | TEAMMEMBERS |
-------------------------------
| Team Xstream | 1351 453 |
| Team Xstream | 976 8762 |
| Team Xstream | 376 2134 |
| Team INsanity | 5463 763 |
| Team INsanity | 87 784 |
| Team INsanity | 187 465 |
| Team INsanity | 761 566 |
Once you have the data, then apply the GROUP_CONCAT() function and GROUP BY the teamname:
select t.teamname,
group_concat(concat(p.FirstNameId, ' ', p.LastNameId) SEPARATOR '/') teamMembers
from teams t
left join teammembers m
on t.teamid = m.teamid
left join people p
on m.peopleid = p.peopleid
group by t.teamname;
See SQL Fiddle with Demo
results:
| TEAMNAME | TEAMMEMBERS |
---------------------------------------------------
| Team INsanity | 761 566/87 784/187 465/5463 763 |
| Team Xstream | 976 8762/376 2134/1351 453 |

Answer 2

You didn't provide information on the table where names are actually stored, but what you are looking for is GROUP_CONCAT function. This is how you would use it to show the first and last name id's. I will leave it to you to join the name table and replace the name id fields in the query with the actual name fields.
SELECT t.TeamName, GROUP_CONCAT(CONCAT(p.FirstNameID, ' ', p.LastNameID))
FROM Teams as t
INNER JOIN TeamMembers as tm on t.TeamID = tm.TeamID
INNER JOIN People as p on tm.PeopleID = p.PeopleID
GROUP BY t.TeamName
By the way, normalizing the names out into their own table and using nameID seems like probably a good example of over normalization. Why not just have name values in People table? This will save you adding a fourth table to your query (and possibly fifth table if first and last names are in different tables).