Question

Given the following table:

InstalledApps

MachineName | AppName | Version
-------------------------------
machine01   | App01   | 1.1
machine01   | App02   | 1.0
machine01   | App03   | 1.5
machine02   | App04   | 2.0
machine02   | App02   | 1.0
machine02   | App01   | 1.1
machine03   | App06   | 7.9.9
machine03   | App01   | 1.1
machine03   | App07   | 11.5
machine03   | App02   | 1.0

I need to select Apps which are common to given “n” machines. It’s an intersect between “n” sets. However, I’m having a hard time coming up with a decent query.

I know that I can do something like this:

SELECT AppName, Version 
FROM InstalledApps 
WHERE MachineName = 'machine01'

INTERSECT

SELECT AppName, Version 
FROM InstalledApps 
WHERE MachineName = 'machine02' 

That will give me

AppName | Version
------------------
App01   | 1.1
App02   | 1.0

However, is there a way I can do it without having to know the number of machines upfront? Something like

SELECT...... 
FROM InstalledApps 
WHERE MachineName IN ('machine01',...'machine99')

Answer 1

I think this should do it for the general case:

SELECT AppName, Version, COUNT(DISTINCT(MachineName)) AS MachineCount
FROM InstalledApps
GROUP BY
  AppName, Version
HAVING
  COUNT(DISTINCT(MachineName)) > 1