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77-424: Access 2013
Topics : Create and manage a database (20–25%) : Protect and maintain a database •Compact databases, repair databases, back up databases, split databases, encrypt databases with a password, merge databases, recover data from backups
Protect and maintain a database
In protecting your data, we look at how to password-protect and encrypt your database to prevent others from opening it either with Access or with another tool. If you’re working with an existing database, clicking Info displays a link to "View and edit database properties", which shows you information about the open database, or to Compact & Repair your database, or to Encrypt the database with a password.
A database can be protected with a password. This prevents unauthorized users from successfully opening the database. As part of the password protection process, the database is encrypted to prevent other software tools from being used to examine the data. To add or remove a password, you must access the database by using a special sequence of steps that will open the database with the Open Exclusive option. You choose a single password for your database, and from that point on it can’t be opened without the password. Even better, the data in your database file is scrambled using a key that’s generated from your password. This ensures that even if high-tech hackers peer directly into your database file with a specialized tool, they won’t be able to retrieve any data. It’s easy to apply a password. :
- Choose File→open. To apply a password, you need to open your database in Exclusive mode. This step is necessary because Access can’t encrypt a database while it’s in use.
- Select the file you want to open, click the drop-down arrow on the open button, and then choose open Exclusive. Access opens the database in Exclusive mode.
- Choose File→Info and click Encrypt with Password. Access asks you to supply a password
- Enter your password, verify it, and then click oK. To ensure that your database is secure, you need to choose a strong password. Good passwords are long (10 letters or more), can’t be found in the dictionary (because attackers use dictionaries to launch automated attacks), use mixed case, and include special characters (like numbers, punctuation, and other . symbols). The password hellodata is a poor choice, while a0nPoTER_wi@t_12 is much more reliable. Access uses the password to encrypt your database and then saves the modified database automatically. Now, the next time you open your database you’ll be asked to supply the password first. If you decide later that you don’t need password protection, choose File→Info and click Decrypt Database.
As changes are made to your data over a period of time, such as when data is deleted or updated, the data will eventually no longer be ordered on the physical storage in the most efficient manner. Over time, as objects are created and removed, the database will also grow in size. Compacting the database reduces the size of the files and makes the database operate faster by reorganizing the physical data. Before you can compact or repair a shared database, you must ensure that no one is using it. The repair operation corrects for any problems in the consistency of the data or indexes in the database. A single process is used to both compact and repair a database. Access is more concerned with getting information in and out of the database as quickly as it canWhy should you care if the file size increases? Here are two reasons:
- A smaller database file runs faster. Performance is a key component to happy database users. You want your forms to load quickly and your queries and reports to run as fast as possible.
- A regularly compacted database is more stable. If the database is used often, compacting regularly helps keep file and table corruption from occurring.
The Compact and Repair command removes the excess. It is good practice to compact your database regularly (once a week is usually fine). Always compact it after making any design changes. Here’s how:
- Open the bloated database and click the Database Tools tab on the Ribbon. The Tools group appears at the very left of the Ribbon.
- Click the Compact and Repair Database button from the Tools group.
compact database file , Follow these steps:
- Click the File tab on the Ribbon.
- Click the Access Options button in the menu bar down the left side of the screen.
- Click Current Database from the list on the left. Options for the current database appear.
- Check the Compact on Close check box.
- Click OK to save your changes.
- Click OK from the resulting message box.
- Close the database and note the lower-right status bar.
back up databases
When using Delete queries, always make sure that you add filter criteria to avoid deleting all the data. After any data is changed by the action queries, you cannot undo the changes. Making a backup copy of the database is recommended before you delete or otherwise modify your data.
Keep a good backup so you can quickly recover missing data and get on with your work. Good backups have no substitute. If you make good backups, the chance of losing data is greatly reduced, your boss promotes you, your significant other unswervingly devotes his or her life to you, and you may even win the lottery. At the very least, you’ll sleep better, knowing that your data is safe.
Splitting the dataset is not as hard as you might think. Access makes it a snap with the Database Splitter Wizard. Follow these steps to split your database:
- Back up the database you’d like to split.
- If necessary, move the database you’d like to split to a folder on your shared drive. This step allows the Database Splitter to set up table links properly for you.
- Open the database file you’d like to split from the shared folder. Make sure you have a backup copy of this database before going any further. Also make sure all database objects are closed.
- Click the Database Tools tab on the Ribbon. The Move Data group appears on the Ribbon. It contains a button called Access Database.
- Click the Access Database button. The Database Splitter Wizard dialog box appears.
- Click the Split Database button and let the wizard do its thing. You will be prompted for a back-end database filename. Enter a name, sit back, and watch the fun unfold before your very eyes.
- Copy the front-end file (the original file you split) to each user’s workstation.
Encripting Database with password
Some programs are intelligent enough to pull the information out of an Access database all on their own. One example is Word, which provides a mail merge feature that lets you take a list of names and addresses from a database, and then use them to create mailing labels, personalized forms, or any other sort of batch paperwork. When using this feature, you don’t need to perform any exporting—instead, you can just point Word to your Access database file. Word Merge. Puts the data into a Word document by using Word’s mail merge feature, which is designed to organize address information into printable labels, envelopes, and form letters. This option isn’t just a straight transfer. Instead, the Word document stores the details about your database (like the name of the database file and the table you’re using),
recover data from backups
CopyDatabaseFile method Gives you a quick way to make a database backup.
If you can’t find the record anywhere, copy the record from a backup of the database file. This solution works only if you’ve backed up your database since the record was originally added. If you back up at night and the record was entered during the same day it went missing, that record will not be in your backup.
Here are some common solutions to unexpected query results:
Check criteria for accuracy. A single misplaced keystroke is all it takes to turn your query into a dud. Check your criteria for spelling or syntax errors — and then run the query again.
Try the Unique Values property. Ever see two copies of each record in your query results when you were expecting just one? A quick fix often comes from using the Unique Values property. This property tells Access to stop with the doubling, already — and, if the query results contain a group of exact duplicates, to return only one row from the group. Here’s how to use this property:
- Open the problem query in Design view. The Design tab on the Ribbon appears.
- Click the Property Sheet button from the tab’s Show/Hide Ribbon group.
- Click in the gray area between the field lists in the top half of the query grid. The Property Sheet should now display Query Properties. (Look right under the Property Sheet’s title bar to confirm this.)
- Click in the Unique Values row of the Property Sheet. A drop-down list arrow appears at the end of the Unique Values row. 5. Select Yes from the drop-down list and run the query.
- Correct the selection logic. Juggling a bunch of AND and OR connections in a query can quickly mess up even the hardiest of database designers.
- Fix table joins. If your query results show way too many records, and the query uses two or more tables, improper joining is the likely cause.
- Check table join types. If your query involves two or more tables, and you get fewer records than you expected, incorrect table joins are the likely cause. For example, if you have an order entry database and run a query listing all customers and their orders, by default, you‘ll see only those customers who have placed an order. To see all customers, whether or not they’ve placed orders, do the following:
- In the Design view, right-click the join (the line connecting the two tables) and choose Join Properties from the menu that appears.
- Examine the types of joins offered and choose the one that says something like "Include ALL records from ‘Customers’ and only those records from ‘Orders’ where the joined fields are equal." The actual text you see differs according to the names of your tables. To query aficionados, this is called an outer join. Very cool.
- Click OK and run the query. You should now have all records from the Customers table whether or not there are corresponding records in the Orders table.
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