Warning: strtotime() [function.strtotime]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 35
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 107
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 109
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 111
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 112
Feb
Warning: strtotime() [function.strtotime]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 35
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 107
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 109
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 111
Warning: date() [function.date]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'America/New_York' for 'EST/-5.0/no DST' instead in /home/frodr/public_html/msofficetuneup.com/wp-includes/functions.php on line 112
04
In the previous example, the Dolls and Manufacturers tables are linked through the Manufacturer field, which stores the name of the manufacturing company. This seems like a reasonable designuntil you spend a couple of minutes thinking about what might go wrong. And databases experts are known for spending entire weeks contemplating inevitable disasters.
Here are two headaches that just may lie in store:
-
Two manufacturers have the same company name. So how do you tell which one made a doll?
-
A manufacturer gets bought out by another company and changes its name. All of a sudden, there’s a long list of records to change in the Dolls table.
You might recognize these problems, because they’re similar to the challenges you faced when you tackled primary keys (Section 2.4). As you learned, it’s difficult to find information that’s guaranteed to be unique and unchanging. Rather than risk problems, you’re better off just relying instead on an AutoNumber field, which stores an Access-generated ID number.
Interestingly enough, you use the same solution when linking tables. To refer to a record in another table, you shouldn’t use just any piece of informationinstead, you should use the unique ID number that points to the right record. Here’s a redesigned Dolls table that gets it right by changing the Manufacturer field to ManufacturerID:
|
ID |
Character |
ManufacturerID |
Purchase Price |
|---|---|---|---|
|
342 |
Yoda |
1 |
$8.99 |
|
343 |
Dick Cheney |
2 |
$28.75 |
|
344 |
Tiger Woods |
1 |
$2.99 |
If you take a look back at the Manufacturers table (Section 5.1.2), then you can quickly find out that the manufacturer with the ID value 1 is MagicPlastic.
This design’s the universal standard for databases. However, it does have two obvious drawbacks:
-
The person adding records to the Dolls table probably doesn’t know the ID of each manufacturer.
-
When you look at the Dolls table, you can’t tell what manufacturer created each doll.
To solve both these problems, use a lookup. Lookups show the corresponding manufacturer information in the Dolls table, and they also let you choose from a list of manufacturers when you add a record or edit the ManufacturerID field. (You saw how to use lookups with value lists in Section 4.4.2. You’ll learn how to use lookups to bring together related tables, like Dolls and Manufacturers, in Section 5.2.)
Tip: For even more power, you can use a join query (Section 6.3). A join query lets you fill in all the manufacturer details alongside the doll information so you can view them side by side.
Popularity: 2% [?]
Recent Comments