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L ISTING 8.1 bookorama.sql—SQL to Create the Tables for Book-O-Rama create table customers customerid int unsigned not null auto_increment primary key, name char30 not null, address cha

You can run an existing SQL file, such as one loaded from the CD-ROM, through MySQL by

typing

> mysql -h host -u bookorama books -p < bookorama.sql

Using file redirection is pretty handy for this because it means that you can edit your SQL in

the text editor of your choice before executing it

L ISTING 8.1 bookorama.sql—SQL to Create the Tables for Book-O-Rama

create table customers

( customerid int unsigned not null auto_increment primary key,

name char(30) not null,

address char(40) not null,

city char(20) not null

);

create table orders

( orderid int unsigned not null auto_increment primary key,

customerid int unsigned not null,

amount float(6,2),

date date not null

);

create table books

( isbn char(13) not null primary key,

author char(30), title char(60), price float(4,2) );

create table order_items

( orderid int unsigned not null,

isbn char(13) not null,

quantity tinyint unsigned,

primary key (orderid, isbn)

);

create table book_reviews

(

isbn char(13) not null primary key,

review text

);

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Each of the tables is created by a separate CREATE TABLEstatement You see that we’ve created each of the tables in the schema with the columns that we designed in the last chapter You’ll see that each of the columns has a data type listed after its name Some of the columns have other specifiers, too

What the Other Keywords Mean

NOT NULLmeans that all the rows in the table must have a value in this attribute If it isn’t

AUTO_INCREMENTis a special MySQL feature you can use on integer columns It means if we leave that field blank when inserting rows into the table, MySQL will automatically generate a unique identifier value The value will be one greater than the maximum value in the column

must be indexed

PRIMARY KEYafter a column name specifies that this column is the primary key for the table Entries in this column have to be unique MySQL will automatically index this column Notice

AUTO_INCREMENT The automatic index on the primary key takes care of the index required by

AUTO_INCREMENT

We have used it here because the primary key for this table consists of the two columns together

UNSIGNEDafter an integer type means that it can only have a zero or positive value

Understanding the Column Types

Let’s take the first table as an example:

create table customers ( customerid int unsigned not null auto_increment primary key, name char(30) not null,

address char(40) not null, city char(20) not null );

When creating any table, you need to make decisions about column types

customerid, is the primary key, which we’ve specified directly We’ve decided this will be an

the auto_incrementfacility so that MySQL can manage these for us—it’s one less thing to

worry about

The other columns are all going to hold string type data We’ve chosen the chartype for these

This specifies fixed width fields The width is specified in the brackets, so, for example,name

can have up to 30 characters

This data type will always allocate 30 characters of storage for the name, even if they’re not

all used MySQL will pad the data with spaces to make it the right size The alternative is

varchar, which uses only the amount of storage required (plus one byte) It’s a small trade

off—varchars will use less space but chars are faster

For real customers with real names and real addresses, these column widths will be far too

narrow

Note that we’ve declared all the columns as NOT NULL This is a minor optimization you can

make wherever possible that also will make things run a bit faster

We’ll talk more about optimization in Chapter 11

Some of the other CREATEstatements have variations in syntax Let’s look at the orderstable:

create table orders

( orderid int unsigned not null auto_increment primary key,

customerid int unsigned not null,

amount float(6,2),

date date not null

);

The amountcolumn is specified as a floating point number of type float With most floating

point data types, you can specify the display width and the number of decimal places In this

case, the order amount is going to be in dollars, so we’ve allowed a reasonably large order total

(width 6) and two decimal places for the cents

The datecolumn has the data type date

In this particular table, we’ve specified that all columns bar the amount as NOT NULL Why?

When an order is entered into the database, we’ll need to create it in orders, add the items to

order_items, and then work out the amount We might not know the amount when the order is

created, so we’ve allowed for it to be NULL

The bookstable has some similar characteristics:

create table books

( isbn char(13) not null primary key,

author char(30), title char(60), price float(4,2) );

8

In this case, we don’t need to generate the primary key because ISBNs are generated elsewhere.

multicolumn primary keys:

create table order_items ( orderid int unsigned not null, isbn char(13) not null,

quantity tinyint unsigned, primary key (orderid, isbn) );

inte-ger between 0 and 255

As we mentioned before, multicolumn primary keys need to be specified with a special pri-mary key clause This is used here

create table book_reviews (

isbn char(13) not null primary key, review text

);

This uses a new data type, text, which we have not yet discussed It is used for longer text, such as an article There are a few variants on this, which we’ll discuss later in this chapter

To understand creating tables in more detail, let’s discuss column names and identifiers in gen-eral, and then the data types we can choose for columns First though, let’s look at the database we’ve created

Looking at the Database with SHOW and DESCRIBE

Log in to the MySQL monitor and use the books database You can view the tables in the data-base by typing

mysql> show tables;

MySQL will display a list of all the tables in the database:

+ -+

| Tables in books | + -+

| book_reviews |

| books |

| customers |

| order_items |

| orders |

+ -+

5 rows in set (0.06 sec)

You can also use show to see a list of databases by typing

mysql> show databases;

You can see more information about a particular table, for example,books, using DESCRIBE:

mysql> describe books;

MySQL will display the information you supplied when creating the database:

+ -+ -+ -+ -+ -+ -+

| Field | Type | Null | Key | Default | Extra |

+ -+ -+ -+ -+ -+ -+

| isbn | char(13) | | PRI | | |

| author | char(30) | YES | | NULL | |

| title | char(60) | YES | | NULL | |

| price | float(4,2) | YES | | NULL | |

+ -+ -+ -+ -+ -+ -+

4 rows in set (0.05 sec)

These commands are useful to remind yourself of a column type, or to navigate a database that

you didn’t create

MySQL Identifiers

There are four kinds of identifiers in MySQL—databases, tables, and columns, which we’re

familiar with, and aliases, which we’ll cover in the next chapter

Databases in MySQL map to directories in the underlying file structure, and tables map to

files This has a direct effect on the names you can give them It also affects the case sensitivity

of these names—if directory and filenames are case sensitive in your operating system,

data-base and table names will be case sensitive (for example, in UNIX), otherwise they won’t (for

example, under Windows) Column names and alias names are not case sensitive, but you can’t

use versions of different cases in the same SQL statement

As a side note, the location of the directory and files containing the data will be wherever it

was set in configuration You can check the location on your system by using the mysqladmin

facility as follows:

mysqladmin variables

8

A summary of possible identifiers is shown in Table 8.4 The only additional exception is that you cannot use ASCII(0) or ASCII(255) in identifiers (and to be honest, I’m not sure why you’d want to)

T ABLE 8.4 MySQL Identifiers

These rules are extremely open

As of MySQL 3.23.6, you can even have reserved words and special characters of all kinds in identifiers, the only limitation being that if you use anything weird like this, you have to put it

in back quotes (located under the tilde key on the top left of most keyboards) For example

create database `create database`;

The rules in versions of MySQL (prior to 3.23.6) are more restrictive, and don’t allow you to

do this

Of course, you should apply common sense to all this freedom Just because you can call a

as in any other kind of programming—use meaningful identifiers

Column Data Types

The three basic column types in MySQL are: numeric, date and time, and string Within each

of these categories are a large number of types We’ll summarize them here, and go into more detail about the strengths and weaknesses of each in Chapter 11

Each of the three types comes in various storage sizes When choosing a column type, the prin-ciple is generally to choose the smallest type that your data will fit into

For many data types, when you are creating a column of that type, you can specify the maxi-mum display length This is shown in the following tables of data types as M If it’s optional for

Optional values throughout these descriptions are shown in square brackets

Numeric Types

The numeric types are either integers or floating point numbers For the floating point

num-bers, you can specify the number of digits after the decimal place This is shown in this book

as D The maximum value you can specify for Dis 30 or M-2(that is, the maximum display

length minus two—one character for a decimal point and one for the integral part of the

num-ber), whichever is lower

For integer types you can also specify if you want them to be UNSIGNED, as shown in

Listing 8.1

For all numeric types, you can also specify the ZEROFILLattribute When values from a

ZERO-FILLcolumn are displayed, they will be padded with leading zeroes

The integral types are shown in Table 8.5 Note that the ranges shown in this table show the

signed range on one line and the unsigned range on the next

T ABLE 8.5 Integral Data Types

Storage

or 0 255

or 0 65535

8388607

or 0 16777215

231

or 0 232

-1

BIGINT[(M)] -263

263

or 0 264

-1

The floating point types are shown in Table 8.6

8

T ABLE 8.6 Floating Point Data Types

Storage

precision floating point numbers

These are equivalent

to FLOAT(4), but with a specified display width and number of decimal places

specified display width and number of decimal places

DOUBLE[(M, D)]

display width

Date and Time Types

MySQL supports a number of date and time types These are shown in Table 8.7 With all

these types, you can input data in either a string or numerical format It is worth noting that a

TIMESTAMPcolumn in a particular row will be set to the date and time of the most recent

opera-tion on that row if you don’t set it manually This is useful for transacopera-tion recording

T ABLE 8.7 Date and Time Data Types

9999-12-31

838:59:59 Note that the range is much wider than you

will probably ever want to use

DATETIME 1000-01-01 A date and time Will be displayed as

00:00:00 YYYY-MM-DDHH:MM:SS.

9999-12-31 23:59:59

TIMESTAMP[(M)] 1970-01-01 A timestamp, useful for transaction

00:00:00 reporting The display format depends on the

value of M(see Table 8.8, which follows)

Sometime The top of the range depends on the limit

timestamps

YEAR[(2|4)] 70–69 A year You can specify 2 or 4 digit format

(1970–2069) Each of these has a different range, as

Table 8.8 shows the possible different display types for TIMESTAMP

T ABLE 8.8 TIMESTAMP Display Types

TIMESTAMP(4) YYMM

TIMESTAMP(2) YY

8

String Types

String types fall into three groups First, there are plain old strings, that is, short pieces of text

types, which we will discuss in more detail in Chapter 11

for example, image or sound data

not Because these column types can hold large amounts of data, they require some special considerations We will discuss this in Chapter 11

val-ues in this column must come from a particular set of specified valval-ues Column valval-ues can contain more than one value from the set You can have a maximum of 64 things in the speci-fied set

the enumeration

We’ve summarized the string data types in Tables 8.9, 8.10, and 8.11 Table 8.9 shows the plain string types

T ABLE 8.9 Regular String Types

[NATIONAL] 1 to 255 Fixed length string of length M, where M

CHAR(M) [BINARY] characters is between 1 and 255 The NATIONAL

key-word specifies that the default character set should be used This is the default in MySQL anyway, but is included as it is part

key-word specifies that the data should be treated as not case insensitive (The default

is case sensitive.)

[NATIONAL] 1 to 255 Same as above, except they are

[BINARY]