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If you don't understand that stuff about AUTO_INCREMENT and PRIMARY KEY, just think of them as giving us a magic way of generating an ID number for each member. It doesn't particularly matter what the values are, as long as they're unique. (When you're ready to learn more about how to declare and use AUTO_INCREMENT columns, Chapter 2, "Working with Data in MySQL," covers them in detail.)
The expiration column is a DATE. It has a default value of '0000-00-00', which is a non-NULL value that means no legal date has been entered. The reason for this is that expiration can be NULL to indicate that a member has a lifetime membership. If we don't specify otherwise, a column that can contain NULL also has NULL as its default value. That's not desirable in this case; if you created a new member record but forgot to specify the expiration date, MySQL would fill in the expiration column with NULL automatically—thus making the member a lifetime member! By specifying that the column has a default value of '0000-00-00' instead, we avoid this problem. That also gives us a value we can search for periodically to find records for which the expiration date was never properly entered.
Now that you've told MySQL to create a couple of tables, check to make sure that it did so as you expect. In mysql, issue the following query to see the structure of the president table:
mysql> DESCRIBE president;
| Field |
Type |
Null |
Key |
Default |
Extra |
| last_name |
varchar(15) |
|
|
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| first_name |
varchar(15) |
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| suffix |
varchar(5) |
YES |
|
NULL |
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| city |
varchar(20) |
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| state |
char(2) |
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| birth |
date |
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0000-00-00 |
|
| death |
date |
YES |
|
NULL |
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