How to design a SQL table where a field has many descriptions - sql

Question

I would like to create a product table. This product has unique part numbers. However, each part number has various number of previous part numbers, and various number of machines where the part can be used.
For example the description for part no: AA1007
Previous part no's: AA1001, AA1002, AA1004, AA1005,...
Machine brand: Bosch, Indesit, Samsun, HotPoint, Sharp,...
Machine Brand Models: Bosch A1, Bosch A2, Bosch A3, Indesit A1, Indesit A2,....
I would like to create a table for this, but I am not sure how to proceed. What I have been able to think is to create a table for Previous Part no, Machine Brand, Machine Brand Models individually.
Question: what is the proper way to design these tables?

Answer 1

There are of course various ways to design the tables. A very basic way would be:
You could create tables like below. I added the columns ValidFrom and ValidTill, to identify at which time a part was active/in use.
It depends on your data, if datatype date is enough, or you need datetime to make it more exactly.
CREATE TABLE Parts
(
ID bigint NOT NULL
,PartNo varchar(100)
,PartName varchar(100)
,ValidFrom date
,ValidTill date
)
CREATE TABLE Brands
(
ID bigint NOT NULL
,Brand varchar(100)
)
CREATE TABLE Models
(
ID bigint NOT NULL
,BrandsID bigint NOT NULL
,ModelName varchar(100)
)
CREATE TABLE ModelParts
(
ModelsID bigint NOT NULL
,PartID bigint NOT NULL
)
Fill your data like:
INSERT INTO Parts VALUES
(1,'AA1007', 'Screw HyperFuturistic', '2017-08-09', '9999-12-31'),
(1,'AA1001', 'Screw Iron', '1800-01-01', '1918-06-30'),
(1,'AA1002', 'Screw Steel', '1918-07-01', '1945-05-08'),
(1,'AA1004', 'Screw Titanium', '1945-05-09', '1983-10-05'),
(1,'AA1005', 'Screw Futurium', '1983-10-06', '2017-08-08')
INSERT INTO Brands VALUES
(1,'Bosch'),
(2,'Indesit'),
(3,'Samsung'),
(4,'HotPoint'),
(5,'Sharp')
INSERT INTO Models VALUES
(1,1,'A1'),
(2,1,'A2'),
(3,1,'A3'),
(4,2,'A1'),
(5,2,'A2')
INSERT INTO ModelParts VALUES
(1,1)
To select all parts of a certain date (in this case 2013-03-03) of the "Bosch A1":
DECLARE #ReportingDate date = '2013-03-03'
SELECT B.Brand
,M.ModelName
,P.PartNo
,P.PartName
,P.ValidFrom
,P.ValidTill
FROM Brands B
INNER JOIN Models M
ON M.BrandsID = B.ID
INNER JOIN ModelParts MP
ON MP.ModelsID = M.ID
INNER JOIN Parts P
ON P.ID = MP.PartID
WHERE B.Brand = 'Bosch'
AND M.ModelName = 'A1'
AND P.ValidFrom <= #ReportingDate
AND P.ValidTill >= #ReportingDate
Of course there a several ways to do an historization of data.
ValidFrom and ValidTill (ValidTo) is one of my favourites, as you can easily do historical reports.
Unfortunately you have to handle the historization: When inserting a new row - in example for your screw - you have to "close" the old record by setting the ValidTill column before inserting the new one. Furthermore you have to develop logic to handle deletes...
Well, thats a quite large topic. You will find tons of information in the world wide web.

Answer 2

For the part number table, you can consider the following suggestion:
id | part_no | time_created
1 | AA1007 | 2017-08-08
1 | AA1001 | 2017-07-01
1 | AA1002 | 2017-06-10
1 | AA1004 | 2017-03-15
1 | AA1005 | 2017-01-30
In other words, you can add a datetime column which versions each part number. Note that I added a primary key id column here, which is invariant over time and keeps track of each part, despite that the part number may change.
For time independent queries, you would join this table using the id column. However, the part number might also serve as a foreign key. Off the top of my head, if you were generating an invoice from a previous date, you might lookup the appropriate part number at that time, and then join out to one or more tables using that part number.
For the other tables you mentioned, I do not see a similar requirement.