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.mdb by visual database manager

Posted on 1998-12-18
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Last Modified: 2010-05-03
Hi

I think Visual Database Manager in VB5 can create and edit a .mdb file. However, after open the add in, I just can not go through the way.
Can you give me the instructions showing the step by step to create a most simple .mdb file with a table?

Victor
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Question by:victorlong
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by:victorlong
ID: 1451274
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mayhew earned 80 total points
ID: 1451275
On the menu select File|New|Microsoft Access|Version x.0 MDB ...

It will ask you where you want to save your new table in a dialog box.  Name your table and save it.

This will bring up "Database Window" and "SQL Statement" windows.  In "Database Window" you'll see a "Properties" field.  Right click on it and select "New Table" from the popup menu.

Then you can type in a table name.  You can press the "Add Field" button to bring up an edit screen for each field you want to add.  You can also create indexes in the bottom part of this window.

When you're done, press the "Build the Table" button and you're set.

Hope this is helpful!  :)

Don
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Author Comment

by:victorlong
ID: 1451276
Hi Mayhew

Yes, I got it by following your instruction. Thank you for your help.

Can you help me more? Can you explain what is the index works and what is it for? (I have increase the point a litile bit.)

Cheers.

Victor
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by:mayhew
ID: 1451277
Hey Victor,

I'm glad that helped!

For the index, I'm not quite understanding your question.  Are you wondering what an index is?  Or how to create one using the Visual Data Manager?  Or something else?

Let me know and I'll be happy to answer your question.  :)

Don
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Author Comment

by:victorlong
ID: 1451278
Hi Mayhew

I agree my question was not very clear since I don't understand index :-)
Can you begin your explanation at why we need index in the table? Then, may be teach me by an example showing the benefit of using index in the table. Or tell me anything you think may help me understan what is the index in the table and why we need that.

Am I asking too much?

Cheers.

Victor
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by:mayhew
ID: 1451279
Hi Victor,

Sorry for the long delay.

Basically, an index is used to improve performance, eg. to make searches go quicker.

When you create an index, you create it for a field or combination of fields that you will be searching on.  For example, in an address book application, you might create an index on a last name field, or a phone number field because those are fields that you typically search on.

I'm not sure of the mechanics for SQL Server or Access, but I can give you a pretty good idea of what's going on in terms of DBase.  Even if the exact process is not the same for MS products, the concept will be similar.

Let's say that you have the following table in DBase:
Name char(15)

with the following data:
Fred
Bob
Hal
Chris

Notice that the records were not entered in alphabetical order.  If you wanted to find the record with a name of 'Chris' you would have to start at the beginning of the table and search through every record until you got to Chris.  For a large table, this can take a lot of time.

(Keep in mind this is an oversimplification)   :)

When you create an index on the <name> field, DBase will create an index file that has sorted pointers to the information in your table.  For example, it might assign the number 1 to Fred, 2 to Bob, 3 to Hal, and 4 to Chris.  Then it would sort them by name and store the numbers in the index file.

For this example your index file would then look something like:
2
4
1
3

Now that the index exists, if you wanted to do a search for the 'Chris' record, you'll end up going through less records because the database engine will use a search algorithm that can take advantage of the fact that your data is sorted.  Thus, your searches will take less time.

You might have heard of 'rebuilding an index'.  What this means is that if new data is entered, (for our example let's say we add 'Al' to our table) that data has to be sorted into the index.

Now our index would look like:
5
2
4
1
3

While indexes will generally improve the performance of a large database, they do increase overhead.  So you need to be careful not to 'over-index' your tables.  Some guidelines to follow are:

Only use indexes on fields that you will be searching on frequently (like name or social security number).

Don't index a field with limited data, for example a boolean field.  You don't get enough increase in performance to justify the overhead.

I hope you find this helpful.  If you have further questions, please feel free to ask.

Don
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Author Comment

by:victorlong
ID: 1451280
Hi mayhew

> Sorry for the long delay.

You must have a very good New Year party :-)

>I hope you find this helpful.

Yes, that is a great help. I believe that I have understanded quite well. Thank you very much.

Victor.
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