How do i concatenate information from a foreign key? - mysql

Question

i just realised i've worded this very poorly
i'm trying to find out if i can do this within an insert statement, not when trying to output the data
This might sound very confusing but hopefully i can explain it.
I have two tables, expertise (parent) and department (child)
In expertise I have :
exp_id int(2) primary key
exp_name varchar(30)
In department I have:
dep_id int(2) primary key
dep_name varchar(30)
exp_id int(2) foreign key
I DO NOT want the outcome for the department rows to look like this:
dep_id dep_name exp_id
1 accounting 32
1 accounting 27
1 accounting 29
I WANT IT to look like this
dep_id dep_name exp_id
1 accounting 32, 27, 29
So there is multiple rows within a row, if that makes any sense.
I believe its concatenation i have to work with, but I've never used this before and was looking for some help
i just realised i've worded this very poorly
i'm trying to find out if i can do this within an insert statement, not when trying to output the data

Answer 1

you should be able to use group_concat, ie:
select dep_id, dep_name, group_concat(exp_id) exp_id
from department
group by dep_id, dep_name
You should also consider normalisation your department table, it is currently violating first normal form due to the repeating groups of dep_id, dep_name. reference here
edit
I see you updated your question to say you want the data stored in this way in the table, not displayed.
The answer to that is: you really don't.
delimited fields are all but impossible to deal with, and are just all around horrible in an rdbms. If you absolutely must have it this way, you could use the above query to create a view, and at least store the real data in a proper, normalised fashion.
To re-iterate. Please don't do this. Kittens will die.

Answer 2

In the spirit of normalized data
-- drop table expertise
create table expertise
( expId int not null,
expName varchar(100) not null
);
insert expertise (expId,expName) values (32,'number massaging');
insert expertise (expId,expName) values (27,'misrepresentation');
insert expertise (expId,expName) values (29,'embezzlement');
-- select * from expertise
-- drop table department;
create table department
( deptId int not null,
deptName varchar(100) not null
);
insert into department (deptId,deptName) values (1,'Accounting');
insert into department (deptId,deptName) values (2,'Executive');
insert into department (deptId,deptName) values (3,'Food Service');
-- select * from department
-- drop table expDeptIntersect;
create table expDeptIntersect
( expId int not null,
deptId int not null
);
insert expDeptIntersect (expId,deptId) values (27,1);
insert expDeptIntersect (expId,deptId) values (32,1);
insert expDeptIntersect (expId,deptId) values (29,1);
--select * from expdeptintersect
select d.deptId,d.deptName,group_concat(i.expId) expId
from department d
join expDeptIntersect i
on i.deptId=d.deptId
group by d.deptId,d.deptName