Using COUNT function to match across multiple columns?

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I'm trying to construct an Oracle SQL query to find matching data in a table across two columns.

I have a large table with the following columns (among others):
'ModuleItemID' [Primary Key int]
'ModuleNumber' [int] column matching to a lookup table of Module Names
'PartNo' column [string]

A single ModuleNumber can be associated with many PartNo's, but each PartNo should only appear with each ModuleNumber once.

I need to root out several instances of PartNos that appear twice with the same ModuleNumber - i.e. "find all ModuleItemID rows with a particular ModuleNumber and PartNo combination where count >1" - but I'm not sure what the exact syntax is.

In the example below, I want to find duplicate rows like 1 & 3 and 7 & 9:

ModuleItemID	ModuleNumber	PartNo
1	1	161-4514
2	1	168-0056
3	1	161-4514
4	2	160-4514
5	2	168-0056
6	3	160-4514
7	3	171-0023
8	3	181-0565
9	3	171-0023

Thank you!

Posted 21-Jun-11 10:37am

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Kschuler · Accepted Answer · 2011-06-21T11:21:00

This should get you a list of Module/Part Numbers and how many times they occur in the table:
SELECT ModuleNumber, PartNo, COUNT(*) as ModulePartCount FROM MyTable GROUP BY ModuleNumber, PartNo

If you only want duplicates, you can add a having clause:
SELECT ModuleNumber, PartNo, COUNT(*) as ModulePartCount FROM MyTable GROUP BY ModuleNumber, PartNo HAVING COUNT(*) > 1

Is that what you are looking for? If not, please state exactly what your end result is supposed to be.