Database

24-Sep-08 9:12

Hi,

Apologies if this is the wrong location for this post.

I have a set of tables say Table A, B & C for simplicity. Table A relates to table B. Table B relates to Table C. No problems so far, however Table A also has related records in Table C. Those records in Table C are marked by not having a value for the the Table B key field.

Now in SQL we can write procedures that handle that but how can we get a .Net DataSet to have a defined relationship when one element is 'the column contains null'?

Obviously we can define another table (D) which just reads in the appropriate records so Table A then joins to Table D but that feels like overkill given that the rest of the table structure is the same.

Regards
Ian Cox Confused | :confused:

Wendelius24-Sep-08 9:31

24-Sep-08 9:31

Perhaps I missed the point but you can define two separate relations using DataRelation class:
- one for table C -> table B
- one for table C -> table A

By default child column can have NULL value unless you define it NOT NULL.

Mika

The need to optimize rises from a bad design

Coxianuk24-Sep-08 10:05

24-Sep-08 10:05

May be I did not get the picture drawn clearly. Using your notation

Table A -> Table B -> Table C
Table A -> Table C

So

Using KeyA, KeyB and KeyC as field names

TableA
KeyA

TableB
KeyA
KeyB

TableC
KeyA
KeyB // Null for records related directly to TableA
KeyC

The first relationship to Table C is therefore possible using KeyA and KeyB from table B
The second is KeyA and null.

Are you saying that I can define the following relationship

ds.Relations.Add("Table A to B",
tableA.Columns["KeyA"], tableB.Columns["KeyA"]);

ds.Relations.Add("Table B to C",
new DataColumn[] {tableB.Columns["KeyA"], tableB.Columns["KeyB"]},
new DataColumn[] {tableC.Columns["KeyA"], tableC.Columns["KeyB"]);

ds.Relations.Add("Table A to C",
new DataColumn[] {tableA.Columns["KeyA"], null},
new DataColumn[] {tableC.Columns["KeyA"], tableC.Columns["KeyB"]);

Hope this better defines my issue.

Wendelius24-Sep-08 10:37

24-Sep-08 10:37

Okay, I jumped into conclusions D'Oh! | :doh:

and didn't think that you would have primary keys that are combined from several fields (if each table would have only one primary key column this wouldn't be any problem).

Anyhow, it could work, but I think that the last relation should be (may have typos):

ds.Relations.Add("Table A to C", 
new DataColumn[] {tableA.Columns["KeyA"], new DataColumn("AlwaysNull", relevantDataType, "NULL")},
new DataColumn[] {tableC.Columns["KeyA"], tableC.Columns["KeyB"]);

The idea is to create a calculated column which always has a vale of null. Haven't tested this though...

Mika

The need to optimize rises from a bad design

Coxianuk24-Sep-08 11:02

24-Sep-08 11:02

I see your logic. Did not think about calculated columns at all. I will try that out later, just looking at something else.

Many thanks
Ian Cox

Wendelius24-Sep-08 11:07

24-Sep-08 11:07

You're welcome. Smile | :)

Mika

The need to optimize rises from a bad design

SQL Server 2000 with SP4 installation problem

nelsonpaixao24-Sep-08 14:47

nelsonpaixao

24-Sep-08 14:47

Listen,

i see you have a column that accepts nulls and is a foregn key?
if so try to use something like this:

SELECT id_client,first_name,isnull(middle_name,'noname'),
last_name FROM dbo.clients

As you see in this case middle_name is varchar like 'noname'.
But sometimes that doesn´t happen

SELECT cl.id_client,cl.first_name,cl.last_name,
isnull(ct.city_postalcode,'nocode') 
FROM dbo.clients as cl inner join dbo.cities as ct 
on ct.id_city = cl.id_city

Here isnull() doesn´t work,(int VS varchar) and you will not get the rows with null values in!!!

What i advice you to do to create a temp table (or not temp), fill the table and display the result, after that delete the table. You code will be larger.
It works fine Cool | :cool:

nelsonpaixao@yahoo.com.br

trying to help & get help

Krishnatv24-Sep-08 6:22

Krishnatv

24-Sep-08 6:22

HI,
I want to install SQL server 2000 in my system.But always iam getting one message it showing

Another instance fo setup is already running

And iam not be able trace what is the reason.

And i want to remove all previous installation entries from Registry.

Through Add/Remove programs i deleted SQL SERVER. From registry how can i delete sql entries.

Thanks in advance.
Rayalu

Re: SQL Server 2000 with SP4 installation problem

Wendelius24-Sep-08 8:38

Small Database Design Confusion

24-Sep-08 8:38

This could be any setup (not necessarily SQL Server). Check processes from Task Manager to see if there's some setup running.

The need to optimize rises from a bad design

oohungoo24-Sep-08 5:16

oohungoo

24-Sep-08 5:16

I am a beginner in designing database. I tried to create 2 tables Users and Topics for a tiny demo forum. The tables are like this:
[tbl_Users]
username
password
email
...

[tbl_Topics]
topicID
title
content
...

1 user can post 0..M topics, 1 topic belongs to only 1 user.
1 user can view 0..M topics (including other's topics). 1 topic can be viewed by 1..M users

I have some questions:
1. Do I have to create a small table name [tbl_User_Topic] between those 2 tables?
2. Do I need to create a UserID field for [tbl_Users] and use this as a primary key instead of username field
3. Should topicID field be auto increament number or just an integer number?
4. If topicID is not an auto number, then what mechanism should I use to create topicID?

Thanks for helping,

Re: Small Database Design Confusion

Wendelius24-Sep-08 8:37

Re: Small Database Design Confusion

24-Sep-08 8:37

oohungoo wrote:
1. Do I have to create a small table name [tbl_User_Topic] between those 2 tables?

If this is one-to-many relationshot, no

oohungoo wrote:
2. Do I need to create a UserID field for [tbl_Users] and use this as a primary key instead of username field

Depends on your design. I would prefer using UserID

oohungoo wrote:
3. Should topicID field be auto increament number or just an integer number?

Again depends on your design. You need the key value so it must get the value from somewhere (identity, custom logic, lookup table...). Identity should be the easiest.

oohungoo wrote:
4. If topicID is not an auto number, then what mechanism should I use to create topicID?

See previous.

Hope this helps,

Mika

The need to optimize rises from a bad design

nelsonpaixao28-Sep-08 14:17

nelsonpaixao

28-Sep-08 14:17

put a id(int) for the user table, and id_user in topic table as well(foregn key). PUT a int id in EVERY table ALLWAYS.

remove password and user name, you are not going to process it are you?

your questions are quite simply i don´t know what to say really.
are you sure that database is that short? if yes keep it can see anything wrong. Unsure | :~

nelsonpaixao@yahoo.com.br

trying to help & get help

SQL Server 2005 Installation Error

Afaak24-Sep-08 4:27

Afaak

24-Sep-08 4:27

Dear ALL,

I am not getting SQL Server Databse files in the installer

It gives only 2 options of SQL Server Native Client & SQL server Setup support files,

i have checked the files & it was installed over my home PC Easily but its not getting successful over my office PC, i have 4, 5 different DVD's of it & tried over 3,4 different PC but not getting the trouble identified , also i have checked added program list in control panel , no SQL instance was found before, kindly help me in this regard.

Re: SQL Server 2005 Installation Error

Wendelius24-Sep-08 8:28

Re: Send Mail Task on Failure

24-Sep-08 8:28

These must be installed before the actual database engine can be installed (in some machines they may already exists in which case this step is skipped). Have you installed those?

The need to optimize rises from a bad design

[Message Deleted]

notes4we24-Sep-08 3:04

notes4we

24-Sep-08 3:04

[Message Deleted]

Wendelius24-Sep-08 8:26

Making a Winform Application Support ORACLE and SQL Server

24-Sep-08 8:26

You could use sysmail_configure_sp with LoggingLevel parameter to get more detailed info on mail queue. Also sysmail_help_queue_sp will give you good info. With these procedures I believe that you can identify where the problem is (in mail queue, in SSIS...)

Also check from history that Send Mail Task is actually run when package fails.

Hope this helps,

Mika

The need to optimize rises from a bad design

Member 118746624-Sep-08 2:40

Member 1187466

24-Sep-08 2:40

I am working on a project to make an existing existing WINFORM application support both Oralce and SQL SERVER.Now it supports SQL server.SO i want the GURUS on codeproject to give me the best suggestions and approaches.We have converted all the existing tables and Stored Procedures into Oracle .The main issues we are having is with the Data types like Money,Date that are incompatible between SQL and Oracle .Since the application is already running in most of our Customer sites, we cannot make changes in UI or Business Logic.We have to handle them efeciently in DAL.Also it has to be compatible with both ORACLE and SQL server .

SO please share me your experiences and Ideas.If you need any furthur Information on specifics please let me know
Thanks in advance
Pankaj

Re: Making a Winform Application Support ORACLE and SQL Server

Coxianuk24-Sep-08 11:23