( Creating tables

Info Catalog ( Creating database ( Database use ( Loading tables
 3.3.2 Creating a Table
 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: 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' data type for the `birth' and `death' columns is
 a fairly obvious choice.
 Once 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.
Info Catalog ( Creating database ( Database use ( Loading tables
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