Re: Odd ListBox behavior with drag/drop enabled - C# Discussion Boards

Database Design Question/Problem

6-Dec-06 10:03

TMATMATMA wrote:
I have a c# form for the user to fill in the registration info. However, the user will get Syntax error (missing operator) in query expression when he fill in the form with

This is because the values are being "injected" into the SQL Command. A very bad practice that leads to innumerable security failures for your database.

Read this article[^] it will tell you exactly why you are getting the problems you are getting and exactly how to fix it.

Upcoming Scottish Developers events:
* We are starting a series of events in Glasgow in 2007. Are you interested in a particular subject, or as a speaker?
* Developer Day Scotland: are you interested in speaking or attending?

My: Website | Blog | Photos

reportviewer

magnifique6-Dec-06 8:37

magnifique

6-Dec-06 8:37

hi folks
how do i set the margin and paper to landscape in the code window with reportviewer
let say am using c#

Re: reportviewer

jdkulkarni6-Dec-06 17:33

jdkulkarni

6-Dec-06 17:33

There is a very good site @ report viewer. http://www.gotreportviewer.com[^] Hopefully this will help. Smile | :)

Jayant D. Kulkarni
Brainbench Certified Software Engineer in C#, ASP.NET, .NET Framework and ADO.NET

mfcuser6-Dec-06 7:11

6-Dec-06 7:11

Since I am new to database, I want to know how to approch that.

Assume that I have a table, I call it table A with the follwoing fields

A | B | C | D
==================================
Now, table A will take value from the fields like
[A1], [B1], [C1], D[1] etc.

Given that for each value added to field A, I want to create another table. For instance, for the above example, I will have a table A1 with fields like
A11 | A12 | A13
===============

The same for A2 etc.

The way to look at it, for each value added to field A of the original table, I want to have another table. I want to know if this is the best way to do it. I couldn't find any other way.

_Zorro_6-Dec-06 7:18

_Zorro_

6-Dec-06 7:18

If the relation is 1 to n then it is ok
Each item of table B would have an index refering to Table A item.

But if it is an n to n relation, then you should have your two tables (A & B) and then a Table C with A & B indexes.

Hope it helps.

mfcuser6-Dec-06 7:26

6-Dec-06 7:26

Only the value from field A determine the next table that will be created. I think this is a 1:n

Colin Angus Mackay6-Dec-06 7:29

6-Dec-06 7:29

mfcuser wrote:
Only the value from field A determine the next table that will be created.

Creating multiple tables in this scenario will hurt the managability of your database. You can do it if you want, but it would create more problems than it solves.

Colin Angus Mackay6-Dec-06 7:27

6-Dec-06 7:27

siskhoalanka wrote:
Each item of table B would have an index refering to Table A item.

No. An index will not help in this situation - it may affect performance, but it will not assist the joining of two tables.

You need a foreign key on table B - and again with your example with the many-to-many join.

Colin Angus Mackay6-Dec-06 7:25

6-Dec-06 7:25

mfcuser wrote:
The way to look at it, for each value added to field A of the original table, I want to have another table.

No - You have a second table that has a foreign key that links it to A. You do not need multiple tables linked to A in this situation.

Table A needs a primary key - this is a column (or group of columns) that uniquely identify a single row in table A.

Table B needs a primary key (pretty much all tables need a primary key) and a foreign key. The foreign key has the same structure as the primary key of the table it links to (in this case table A). So, for example, if the PK of table A is an integer the foreign key on Table B that links to table A must also be an integer.

When you insert rows in Table B that link back to Table A then you put into the foreign key the value of the primary key of the row in A that you want to link to.

Does this help?

Colin Angus Mackay6-Dec-06 7:30

6-Dec-06 7:30

You may also consider that this type of question may be better asked in the SQL forum in future - You will get a greater number of people who know databases better than here - although the majority of C# developers will also know how databases work.

mfcuser6-Dec-06 7:49

6-Dec-06 7:49

Thank you for your input, but I am a beginner in sql. The way to look at it, in a long term. Will not be manageable, but it is easier for me to understand.

Again, lets look at it in terms of matrix

Table A = [A1 A2 A3 A4];
Inside table A, we can have something like that
A1 A2 A3 A4
===================
a b c d
e f g h

now I have two table

Table a and table e with fields on their onw

another way to look at it, if I have two table A and B. If I look at the contain of field A1 to enter data on table B. I cannot do that by row, because some of the field will be blank. Keep in mind I don't have much knowledge on database.

Colin Angus Mackay6-Dec-06 8:01

6-Dec-06 8:01

mfcuser wrote:
Again, lets look at it in terms of matrix

Table A = [A1 A2 A3 A4];
Inside table A, we can have something like that
A1 A2 A3 A4
===================
a b c d
e f g h

now I have two table

Table a and table e with fields on their onw

I don't see a table a and table e - I see two rows where colum A1 has a value of "a" in one row and "e" in the other row.

mfcuser wrote:
if I have two table A and B. If I look at the contain of field A1 to enter data on table B. I cannot do that by row, because some of the field will be blank. Keep in mind I don't have much knowledge on database.

This confuses me even more because I have no idea what you are describing.

Why not drop the A, B, etc. and use a real world example? It is less abstract and easier to understand.

mfcuser6-Dec-06 8:37

6-Dec-06 8:37

I am just brainstorming the design. What I said, you have table A inside table A you have fields A, B, C, D.

Now, inside field A, you have data A1, A2, A3 etc. You can call them rows as well. Now, I want to create new tables for those fields. For example, I will have three new tables: A1, A2, A3. The way to look at it, for each value in field A, I have a new table or you can call it for each row.

I don't think this is a good design, but it is simpler for me to understand.

This may have a similarity, but I don't hink it is the same as what I want to do. Assume that you have a table for customers; you also have a table for customer order. I can see there is a relationship between these two tables.

This is what I really like to do, but I don't know if database allows you to do that. Can you have a table inside a table? If you look at it in a spreasheet form like a grid. You can click on one cell and have another grid open.

Colin Angus Mackay6-Dec-06 9:35

6-Dec-06 9:35

mfcuser wrote:
What I said, you have table A inside table A you have fields A, B, C, D.

You cannot nest tables. You cannot have one table inside another table.

You can have related tables. Table A is related to Table B.

mfcuser wrote:
Now, inside field A, you have data A1, A2, A3 etc.

You mean there are a number of rows, and for each row column A will contain data such as A1, A2, A3, etc. (Please try and pick up the correct terminology - it will make things much easier).

mfcuser wrote:
Now, I want to create new tables for those fields. For example, I will have three new tables: A1, A2, A3. The way to look at it, for each value in field A, I have a new table or you can call it for each row.

This is very unwise. As I have suggested before you have 2 tables. Table A and Table B. You filter the result of table B on its foreign key (which is the link to table A).

mfcuser wrote:
This is what I really like to do, but I don't know if database allows you to do that. Can you have a table inside a table?

No, you cannot - you relate them as I've mentioned previously.

One customer can have many orders

Customer Table:
Id, FirstName,  Surname, ....
------------------------------
 3, Joe,        Bloggs, ....
 5, Sarah-Jane  Smith, ....
 
CustomerOrder Table:
Id, CustomerId, OrderDate,  DispatchDate, ....
------------------------------------------
 1, 3,          2006-12-01, 2006-12-06, ....
 2, 5,          2006-12-02, 2006-12-06, ....
 3, 3,          2006-12-06, -null-, ....

We see here that Joe Bloggs has made 2 orders.

They can be joined together like this:

SELECT FirstName, Surname, OrderDate, DispatchDate
FROM Customer
INNER JOIN CustomerOrder ON Customer.Id = CustomerOrder.CustomerId

which will return

FirstName,  Surname, OrderDate,  DispatchDate
--------------------------------------------
Joe,        Bloggs,  2006-12-01, 2006-12-06
Sarah-Jane, Smith,   2006-12-02, 2006-12-06
Joe,        Bloggs,  2006-12-06, -null-

mfcuser6-Dec-06 10:08

6-Dec-06 10:08

In that case I assume I have to identify primary key and set a relationship