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(mysql.info)Creating tables

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Creating a Table
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Creating the database is the easy part, but at this point it's empty, as
`SHOW TABLES' will tell you:

     mysql> SHOW TABLES;
     Empty set (0.00 sec)

The harder part is deciding what the structure of your database should
be: what tables you will need and what columns will be in each of them.

You'll want a table that contains a record for each of your pets.  This
can be called the `pet' table, and it should contain, as a bare minimum,
each animal's name.  Because the name by itself is not very
interesting, the table should contain other information.  For example,
if more than one person in your family keeps pets, you might want to
list each animal's owner.  You might also want to record some basic
descriptive information such as species and sex.

How about age?  That might be of interest, but it's not a good thing to
store in a database.  Age changes as time passes, which means you'd
have to update your records often.  Instead, it's better to store a
fixed value such as date of birth.  Then, whenever you need age, you
can calculate it as the difference between the current date and the
birth date.  MySQL provides functions for doing date arithmetic, so
this is not difficult.  Storing birth date rather than age has other
advantages, too:

   * You can use the database for tasks such as generating reminders
     for upcoming pet birthdays.  (If you think this type of query is
     somewhat silly, note that it is the same question you might ask in
     the context of a business database to identify clients to whom
     you'll soon need to send out birthday greetings, for that
     computer-assisted personal touch.)

   * You can calculate age in relation to dates other than the current
     date.  For example, if you store death date in the database, you
     can easily calculate how old a pet was when it died.

You can probably think of other types of information that would be
useful in the `pet' table, but the ones identified so far are
sufficient for now: name, owner, species, sex, birth, and death.

Use a `CREATE TABLE' statement to specify the layout of your table:

     mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
         -> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);

`VARCHAR' is a good choice for the `name', `owner', and `species'
columns because the column values will vary in length.  The lengths of
those columns need not all be the same, and need not be `20'.  You can
pick any length from `1' to `255', whatever seems most reasonable to
you.  (If you make a poor choice and it turns out later that you need a
longer field, MySQL provides an `ALTER TABLE' statement.)

Animal sex can be represented in a variety of ways, for example, `"m"'
and `"f"', or perhaps `"male"' and `"female"'.  It's simplest to use
the single characters `"m"' and `"f"'.

The use of the `DATE' data type for the `birth' and `death' columns is
a fairly obvious choice.

Now that you have created a table, `SHOW TABLES' should produce some
output:

     mysql> SHOW TABLES;
     +---------------------+
     | Tables in menagerie |
     +---------------------+
     | pet                 |
     +---------------------+

To verify that your table was created the way you expected, use a
`DESCRIBE' statement:

     mysql> DESCRIBE pet;
     +---------+-------------+------+-----+---------+-------+
     | Field   | Type        | Null | Key | Default | Extra |
     +---------+-------------+------+-----+---------+-------+
     | name    | varchar(20) | YES  |     | NULL    |       |
     | owner   | varchar(20) | YES  |     | NULL    |       |
     | species | varchar(20) | YES  |     | NULL    |       |
     | sex     | char(1)     | YES  |     | NULL    |       |
     | birth   | date        | YES  |     | NULL    |       |
     | death   | date        | YES  |     | NULL    |       |
     +---------+-------------+------+-----+---------+-------+

You can use `DESCRIBE' any time, for example, if you forget the names of
the columns in your table or what types they are.