Sql-server – How would i create a report involving multiple many to many relationships

Situation 1:

Your tables have one relationship and not two. (example: a Device belongs to a DeviceType)

So, keep only one relationship, the one with the composite keys (that include the Primary Key). The other relationship is redundant when the composite one is defined.

I would also suggest you have same names for related columns:

DeviceCategory Table
CategoryCode | Name        | Description
----------------------------------------
WKS          | Workstation | Description of what classifies an item as a workstation...
LPT          | Laptop      | Description of what classifies an item as a laptop...

DeviceType Table
DeviceTypeID | CategoryCode | Manufacturer | Model  | IsTrackedInOtherSystemDefault
-----------------------------------------------------------------------------------
1            | WKS          | Dell         | GX1000 | true
2            | LPT          | HP           | dv4000 | false
3            | WKS          | HP           | xx9000 | false

Device Table
DeviceID | SerialNumber | DeviceTypeID | IsTrackedInOtherSystem | CategoryCode 
------------------------------------------------------------------------------
1        | I81U812      | 1            | true                   | WKS
2        | N0S4A2       | 1            | false                  | WKS
3        | 3BL1NDMIC3   | 2            | false                  | LPT

So, the design would be:

DeviceCategory
--------------
CategoryCode   PK
Name           U1
Description

DeviceType 
----------
DeviceTypeID   PK   U1
CategoryCode   FK   U1
Manufacturer   U2
Model          U2
IsTrackedInOtherSystemDefault

Device 
------
DeviceID       PK   U1
SerialNumber   U2
DeviceTypeID   FK1
IsTrackedInOtherSystem
CategoryCode   FK1  U1

and for the Computer:

Computer
--------
DeviceID       PK   FK1
Hostname       U1
IPAddress      U2
CategoryCode   FK1  CHK

The "additional" UNIQUE keys (the two composite U1 ones) will be needed in most DBMS to enforce the foreign key constraints. I guess this answers your question 2, relationships needs indices to be enforced, so (you have to) use them. They will be used by the DBMS not only to enforce integrity but in your queries/statements, when you will be joining the tables.

The only one that is not needed is the U3 you had in the Computer table.

About question 3 (the over-engineering part): No, I don't think so but that's just my opinion. And you haven't told us if this is a homework/exercise or a real project, whether you will be holding only your family's or a multi-million company's inventory, etc.

Situation 2

I think what you have is fine and there is no need (and not a good idea) to have referential integrity constraints on these columns. This is a default value that is copied in the second table via a stored procedure (I guess during Inserts on the second table?) or altered by a user. If you add an FK, won't that deny users the ability to override the default?

The names of the two columns are self-explanatory enough for a DBA to understand the functionality.

This sounds like a really simply one-to-many relationship.

For SQL Server, I would write this like:

CREATE TABLE Devices
(
    DeviceID INT
    , DeviceName nvarchar(255)
);

CREATE TABLE Cards
(
    CardID INT
    , CardName nvarchar(255)
    , DeviceID INT
);

CREATE TABLE Ports
(
    PortID INT
    , PortName nvarchar(255)
    , CardID INT
);


INSERT INTO Devices VALUES (1, 'Test Device 1');
INSERT INTO Devices VALUES (2, 'Test Device 2');
INSERT INTO Cards VALUES (1, 'Card 1 in Test Device 1', 1);
INSERT INTO Cards VALUES (2, 'Card 2 in Test Device 1', 1);
INSERT INTO Cards VALUES (3, 'Card 1 in Test Device 2', 2);
INSERT INTO Cards VALUES (4, 'Card 2 in Test Device 2', 2);
INSERT INTO Ports VALUES (1, 'Port in Card 1, Device 1', 1);
INSERT INTO Ports VALUES (2, 'Port in Card 2, Device 2', 4);

SELECT *
FROM Devices;

SELECT *
FROM Cards;

SELECT *
FROM Ports;

This allows a Device to have multiple Cards, which in turn can have multiple Ports.

The results:

The 3 tables can be JOINed together like this:

SELECT DeviceName, CardName, PortName
FROM Devices 
    INNER JOIN Cards ON Devices.DeviceID = Cards.DeviceID
    INNER JOIN Ports ON Cards.CardID = Ports.CardID
ORDER BY DeviceName, CardName, PortName;

If you use LEFT JOIN like this:

SELECT DeviceName, CardName, PortName
FROM Devices 
    LEFT JOIN Cards ON Devices.DeviceID = Cards.DeviceID
    LEFT JOIN Ports ON Cards.CardID = Ports.CardID
ORDER BY DeviceName, CardName, PortName;

you get these results:

This is an image showing the table relationships: