Mysql your visual blueprint for creating open source databases- P13 ppt

›Type mysql_query to begin the function that sends the query to the MySQL server, and add the query and a variable to store the result identifier.. To use this function, specify the data

■ The System variables and

their values are displayed

ˇClick the Home link

to return to the main phpMyAdmin page

ÁClick the Show processes link

■ The MySQL server's current process list is displayed

‡Click the Home link to return to the main phpMyAdmin page

When you select the Users option, the user table in the mysql

database is opened, and the list of current users is displayed The Edit link next to each username allows you to change the user's hostname and assign privileges The Delete link deletes a user The Grants link displays the current list of privileges granted to a user, and allows you

to delete or modify the privileges.

The Users page also includes a form that allows you to create a new user You can specify the hostname the user is allowed to connect from, a password, and the privileges the user should be assigned for

a particular database.

You can also open the mysqldatabase directly in phpMyAdminto work with the various security tables Keep in mind that this feature

is potentially dangerous; if you mistakenly delete the root user, for example, you can lose access to the server See Chapter 11 for more information about managing MySQL security.

For details on using phpMyAdminto manage a MySQL server, see the official documentation The complete phpMyAdmindocumentation is usually installed when you set up this utility To access your local copy

of the documentation, follow the phpMyAdmindocumentation link

on the main page.

227

⁄Type <?php to start the

PHP script

Note: You will usually want to include basic HTML tags, as shown here

¤Type mysql_connect( to begin the command

Before you can use any MySQL functions in PHP, you

must first open a connection to the MySQL server.

You can do this using the mysql_connectfunction.

To use this function, specify a hostname, username, and

password for the MySQL server:

$link=mysql_connect("localhost", "testuser",

"testpw");

This command opens a connection to the MySQL server

and returns a link identifier that can be used to perform

operations on the server In this example, the identifier is

stored in the $linkvariable If the connection to the server

is not opened successfully, the boolean value falseis

returned, and an error message is displayed.

If you do not specify one or more of the parameters for the

mysql_connectcommand, PHP assumes default values It

attempts to use localhostas the server hostname, the

username the Web server uses for PHP, and no password If these values do not work on your MySQL server, an error will be returned unless you specify a valid hostname, username, and password.

After you have opened a connection to the MySQL server, you can use the connection throughout the PHP script If you only have a single connection to a single server open, you can use it without needing the link identifier.

The connection to the MySQL server stays open until your PHP script ends, or until you explicitly close the connection.

To close a connection, use the mysql_closecommand and specify the link identifier returned when you opened the connection This command closes the link opened by the previous example:

mysql_close($link);

CONNECT TO A MYSQL SERVER

228

CONNECT TO A MYSQL SERVER

‹Add the hostname,

username, and password

for your MySQL server

Note: See Chapter 11 for information

on creating a username and

password

›If desired, add a variable

to store the link identifier returned by mysql_connect

ˇEnd the command with

a closing parenthesis and a semicolon, and press Enter

ÁType ?> to end the script

Note: Add any commands to work with the server before this tag

■ This completes the PHP script to connect to MySQL

MySQL also supports persistent connections This is a special type of

connection that stays open even after the PHP script ends If the same user attempts to connect to the server a second time, PHP finds the existing connection and returns its identifier rather than returning a new connection.

To use persistent connections, use mysql_pconnect()to open the connection The arguments for this function are the same as for the standard mysql_connect()function You cannot close a persistent connection manually; instead, the server will keep the connection open until MySQL's wait_timeoutperiod expires See Chapter 10 for information on setting this timeout value on a MySQL server.

Example:

$link=mysql_pconnect("localhost", "testuser", "testpw");

// Add statements that use the database server here

Persistent connections can be more efficient in an application where the same user will make many queries on different PHP scripts In a simple application, they are less efficient because connections are left open and not used further, and MySQL may run out of connections for future clients.

Persistent connections only work if PHP is running as a module on an Apache Web server They are not currently supported when PHP is run as a CGI program or on other Web servers.

229

Note: Start with a basic HTML

document

⁄Type <?php and ?> to

begin and end the PHP script

¤Type mysql_connect

to begin the statement that connects to the database, and add the details for the server, username, and password

‹Type mysql_select_db

followed by the database name to select the database for future queries

›Type mysql_query to begin the function that sends the query to the MySQL server, and add the query and a variable to store the result identifier

After you have connected to the MySQL server from a

PHP script, you can run one or more MySQL queries.

Often, you will want to send a SELECTquery to the

server and display the resulting data PHP includes a

number of ways to receive data from the SQL server.

As with the MySQL monitor, before you can make a query,

you must select a database To do this, use the mysql_

select_dbfunction To use this function, specify the

database name as a string:

mysql_select_db("testdb");

After you have selected a database, you can send an SQL

query to the server using the mysql_queryfunction To

use this function, specify the query as a string The following

example sends a simple SELECTquery to the server:

$result=mysql_query("SELECT quote, author

FROM quotes");

If the query is successful, the mysql_queryfunction

returns a result identifier In this example, the $result

variable stores the result identifier You can use this

identifier later in the script to display the query results.

While the result identifier indicates that the query was successful, this only means that MySQL understood the query — it does not mean there are definitely one or more rows of data in the result If the query is unsuccessful, the

mysql_queryfunction returns a FALSEvalue instead Some queries, such as INSERTand DELETE, do not return data from the server In this case,mysql_querysimply returns TRUEif the query was successful.

To display query results, you can use the mysql_fetch_row

function This function accepts a result identifier, and returns the next row of the result as an array The array includes all of the columns of the result in order You can repeat the function to retrieve all of the result rows The following example uses a whileloop to retrieve all of the rows:

while(list($quote, $author) = mysql_fetch_row($result)) { echo "<p>$quote $author</p>"; }

This example retrieves each row into the $quoteand

$authorvariables These are used with an echostatement

to display each row as an HTML paragraph The list

function allows the array returned by mysql_fetch_row

to be stored in two regular variables instead of an array, and

is a convenient way to handle simple queries.

DISPLAY QUERY RESULTS

230

DISPLAY QUERY RESULTS

ˇType while to begin

the loop, and add the

mysql_fetch_row

statement Include braces

to enclose the loop

ÁType echo to begin the statement that displays each row Add the string to display and a closing bracket to end the loop

‡Load your PHP document into a Web browser

■ The rows of data are displayed within the HTML document

Note: This example uses the quotes table in the testdb database You can import this table from the CD-ROM

You can optionally specify a link identifier from mysql_connectas

a second parameter to the mysql_select_dband mysql_query

functions However, these and most other MySQL functions in PHP default to using the last connection you opened, so this is usually not necessary.

You can use the mysql_db_queryfunction to avoid selecting a database first This function is similar to mysql_query, but accepts a database name as its first parameter.

To use this script or any PHP script you create, you must first save the edited file, and then upload it to your Web server that supports PHP.

If you are using PHP version 3, save the file with the php3 extension.

For PHP version 4, save the file with the php extension.

After the file is saved, you will need to upload it to the correct directory of the Web server You can do this using the same program you use to upload HTML documents Typically this is done using the FTP protocol.

After the file is uploaded to the server, you can use a Web browser to display the result PHP does not require a particular browser because

it creates HTML output PHP pages display just like HTML pages.

231

Note: Start with a basic HTML

document

⁄Type <?php and ?> to

begin and end the PHP script

¤Type mysql_connect

followed by the correct user, password, and hostname to connect to the database

‹Type mysql_select_db

followed by the database name to select the database for future queries

›Type $result = mysql_query

to begin the function that sends the query to the MySQL server, and add the query in quotation marks Note: This example uses the quotes table in the testdb database You can import this table from the CD-ROM

When you use the mysql_fetch_rowfunction to

retrieve rows from a query, you must specify the column names in the query and retrieve them in the same order If you are trying to use a query that returns

all columns of a table, and are unsure of the order the

columns will be returned in, you can use mysql_fetch_

objectinstead.

For example, suppose you have made the following query

to the MySQL server This query retrieves all columns and

all rows from the quotes table.

$result=mysql_query("SELECT * FROM quotes");

To retrieve the data, you can use mysql_fetch_object.

This returns an object whose properties are the column

values for the row Thus, you can refer directly to the

MySQL column names rather than assigning your own

variable names to each column The following whileloop

uses the mysql_fetch_objectfunction to retrieve and

display each row:

while($row = mysql_fetch_object($result)) { echo "<p>$row->quote $row->author</p>"; }

In this example, the $rowvariable stores each row You can use the ->operator to refer to each MySQL column name

as a property of the object Thus, you can refer to the quote column as $row->quoteand the author column as

$row->author Because the MySQL query specified the wildcard

*rather than specific column names, all columns of the table are available from the object.

You can use whichever function you are most comfortable with to return data from a MySQL query The data returned

is the same; only the method you use to access it changes PHP includes several other fetchcommands that return the results in different formats, such as mysql_fetch_assoc

to store the data in an associative array This type of array uses column names to index the results rather than numeric indexes.

STORE QUERY RESULTS AS OBJECTS

232

STORE QUERY RESULTS AS OBJECTS

ˇType while to begin the

loop that iterates through

the rows of data Add the

statement to retrieve a row

and an opening brace to

begin the loop

ÁType echo followed by a string using the $row object

to display the row Add the closing brace to end the loop

‡Load your PHP document into a Web browser

■ The rows of data are displayed within the HTML document

If you are running into MySQL errors while attempting to use a database from PHP, it is useful to display the results within your PHP script The following PHP script adds ifstatements to check whether each MySQL command succeeded It displays an appropriate error message if any command fails.

Example:

<?php

$link = mysql_connect("localhost", "testuser", "testpw");

if (!$link) echo "Failed to connect to MySQL server!";

$status=mysql_select_db("testdb");

if (!$status) echo "Failed to select database!";

$result=mysql_query("SELECT * FROM quotes");

if (!$result) echo "The MySQL query failed!";

while($row = mysql_fetch_object($result)) { echo "<p>$row->quote $row->author</p>"; }

?>

This example checks the results of the mysql_connect,mysql_select_db,

mysql_query, and mysql_fetch_objectcommands All of these return a

FALSEvalue if they fail The one condition that these do not account for is if the query succeeds but returns a zero-row result If this happens, the while

loop will end immediately without displaying any data.

233

Note: Start with a basic HTML

document

⁄Type <?php and ?> to

begin and end the PHP script

¤Type mysql_connect

followed by the username, host, and password to connect

to the MySQL server

‹Type mysql_select_db

followed by the database name to select the database

Note: This example uses the testdb database and the scores table You can import this table from the CD-ROM

›Type $query= followed

by the MySQL query in quotation marks

ˇType $success = mysql_query ($query); to create the statement that sends the query to the server

You can use the mysql_querycommand in PHP to

send an INSERTquery to the MySQL server When

you do this, a result identifier is not returned because

an INSERTquery does not return any data from the MySQL

server Instead, the result returned from mysql_queryis a

simple trueor falsevalue that indicates whether the

query was successful.

For example, the following PHP statements add a record to

the scores table and display a message indicating success or

failure:

$query="INSERT INTO scores (name, score)

VALUES ('Fred', 92)";

$success = mysql_query($query);

if ($success) echo "The INSERT query was

successful.";

else echo "Error: INSERT query failed.";

This example stores the query in the $queryvariable, and

then uses the mysql_queryfunction to send the query to

the MySQL server The result of the query is stored in the

$successvariable The ifstatement checks this variable and displays a success message, and the elsestatement displays an error message if the insert was unsuccessful Unlike SELECTqueries, an INSERTquery does not return a result identifier The result stored in the $successvariable will be a simple TRUEor FALSEvalue.

As with other MySQL queries, you must first connect to the MySQL server using the mysql_connectfunction, and then select a database with mysql_select_dbbefore attempting to insert a row You must be connected using a MySQL username that has the INSERTprivilege for the table you are using in the INSERTcommand.

Because double quotation marks are used to define the

$querystring, you cannot use double quotes inside the query You can substitute single quotation marks within the query Only values to be stored in text columns need to be quoted You can use a PHP variable within the INSERT

query by including its name in the $querystring.

INSERT A RECORD FROM PHP

234

INSERT A RECORD FROM PHP

ÁType if to begin the

statement that checks whether

the query succeeded, followed

by echo and the success

message in quotation marks

‡Type else to begin the statement that checks for an error, and type echo followed

by the error message

°Load the PHP document into a Web browser

■ The displayed message indicates whether the INSERT query was successful

If a table includes an auto-increment column, it will automatically be updated with a new unique value each time you insert a record After you have inserted a row into a table from PHP, you can use the mysql_insert_idfunction to find out what number was assigned to the auto-increment field in the INSERTquery.

This technique is useful because you now have a value that you can use to find the inserted row in a subsequent query Without this feature, you would have to use a separate query to find the newest row, and even that may find a row inserted by a different user.

For example, the following PHP code inserts a row into the quotes table and then displays the ID assigned to the auto-increment field.

Example:

$link=mysql_connect("localhost", "testuser", "testpw");

mysql_select_db("testdb");

$query = "INSERT INTO quotes (quote, author) VALUES ";

$query = "('Union gives strength.', 'Aesop')";

$success = mysql_query($query);

if ($success) { echo "The INSERT query was successful.";

echo "The record number is: " + mysql_insert_id();

} else echo "Error: INSERT query failed.";

You can optionally specify a link identifier from mysql_connectwith the mysql_insert_id

function If you do not use an identifier, the most recent connection used is assumed.

235

Note: Start with a basic HTML

document

Note: This example uses the scores

table in the testdb database

⁄Type <?php and ?> to

begin and end the PHP script

¤Type mysql_connect

followed by the username, password, and hostname to connect to the MySQL server

‹Type mysql_select_db

followed by the database name to select the database

›Type $query= followed by the DELETE query

ˇType $success=mysql_ query($query); to send the query to the server

You can also use PHP to send a DELETEquery to the

MySQL server As with an INSERTquery, when you

use the mysql_queryfunction with a DELETE

query, a simple trueor falseresult is returned that

indicates whether the delete was successful.

To delete one or more rows of a table, you usually will need

to specify a WHEREclause Without this clause, all records of

the table would be deleted The following PHP statements

send a DELETEquery to the MySQL server:

$query="DELETE FROM scores WHERE name =

'fred'";

$success=mysql_query($query);

if ($success) echo "The DELETE query was

successful.";

else echo "Error: DELETE query failed.";

These statements store the query in the $queryvariable and send it to the MySQL server using the mysql_query

function The ifstatement displays a message if the

DELETEquery succeeded, and the elsestatement displays

a message if the query failed.

Note that a failed query is not the same as a nonmatching

WHEREclause If the WHEREclause does not match any records, the mysql_queryfunction will still succeed The query will only fail if the server cannot be reached, or if there is a syntax error in the query.

You can find out how many rows were affected by the

DELETEquery with the mysql_affected_rowsfunction This function returns the number of rows affected by the most recent DELETE,INSERT, or UPDATEquery You can use this to determine how many rows the WHEREclause matched.

DELETE RECORDS USING PHP

236

DELETE RECORDS USING PHP