Question

first question from me and it’s a bit of a complex one, so do guide me through any etiquette you’re all used to! Right, bit of a complex one here so I shall describe what I want first before going into code.

MySQL database, I have a table of organisations, a table of services, and a table that cross-references organisations with services. I’m building a search function that will retrieve the organisations that match ANY selected services, but will sort them based on how many services they match AND list what those services are.

OK, the pertinent bits of code n whatnot:

Organisations table (organisations):

id:   INT, AI
name: VARCHAR(150)

Services table (services):

id:   INT, AI
name: VARCHAR(150)

Cross-reference table (xref_org_services):

org_id:     INT
service_id: INT

I can get a list of organisations that match any of the services I search for:

SELECT DISTINCT organisations.name AS org
FROM organisations
JOIN xref_org_services ON organisations.id=xref_org_services.org_id
WHERE xref_org_services.services_id IN (x, y, z)
ORDER BY org ASC

where x, y, z would be the ID of the services I’ve selected. Done, not a problem.

Now I want to return how many services each of the organisations match, and what they are. I’ve had a try with

SELECT organisations.name AS org, COUNT(xref_org_services.services_id) AS matched

but that’s giving me the number of rows matched total which isn’t what I want. Am I looking at a nested SELECT somewhere to do the count?

Ultimately, my output needs to go something like this:

Org_1 matched 4 services
    - Serv_1
    - Serv_3
    - Serv_4

Org_2 matched 3 services
    - Serv_1
    - Serv_2
    - Serv_4

Org_3 matched 1 service
    - Serv_2

Am I making any sense at all? Let me throw some “data” into this then to see if I can clarify things a bit.

organisations:

id  |  name
-------------------------
1   |  A1 Train
2   |  Faux LLC
3   |  Shakey Practice

services:

id  |  name
-------------------------
1   |  PTS
2   |  Track safety
3   |  Assessors
4   |  Structural
5   |  Signalling

xref_org_services:

org_id  |  services_id
-------------------------
1   |  1
1   |  2
1   |  4
2   |  1
2   |  4
3   |  5

So, this means:

• A1 Train offers PTS, Track Safety and Structural
• Faux LLC offers PTS and Structural
• Shakey Practice offers Signalling

If I want to retrieve all organisations that offer PTS, Track Safety and Structural I want the output to say something along the lines of:

A1 Train matched
    - PTS
    - Track Safety
    - Structural

Faux LLC matched
    - PTS
    - Structural

I hope this makes sense. Pointers, hints, full answers all welcome. Let me know if you need clarifications or further information.

Thanks

Answer 1

You want to use GROUP BY:

SELECT
  organisations.name AS org,
  COUNT(*) AS matched,
  GROUP_CONCAT(services.name SEPARATOR "\n") AS services
FROM
  organisations
  LEFT JOIN xref_org_services
    ON xref_org_services.org_id = organisations.id
  LEFT JOIN services
    ON services.id = xref_org_services.services_id
WHERE xref_org_services.services_id IN (x, y, z)
GROUP BY organisations.id
ORDER BY org ASC;