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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 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.)
Several types of values can be chosen to represent sex in animal records,
such as "m"
and "f"
, or perhaps "male"
and "female"
. It's simplest
to use the single characters "m"
and "f"
.
The use of the DATE
datatype 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 have.
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