Syntax

DELETE FROM table_name
WHERE some_column = some_value

Again we used WHERE clause here in the DELETE syntax. The WHERE clause specifies which record or records that should be deleted. If you omit the WHERE clause, all records will be deleted.

For eg:

Country Capital
Zimbabwe Harare
Poland Warsaw

<?php
$conn = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
mysql_query(”DELETE FROM Country WHERE Capital=’Warsaw’”);
mysql_close($conn);
?>

After the deletion, the table will look like this:

Country	Capital
Zimbabwe	Harare

Syntax

UPDATE table_name
SET column1=value, column2=value2,…
WHERE some_column=some_value

WHERE clause is included in the update statement to conditionally update the records. It specifies which record or records should be updated. If there is no WHERE clause, all records will be updated.

For eg:

Zimbabwe Harare
Poland Warsaw

The following example updates some data in the “Country” table:

<?php
$con = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $con);
mysql_query(”UPDATE Country SET Capital = ‘Poland’
WHERE FirstName = ‘Poland’”);
mysql_close($conn);
?>

After the update, the “Country” table will look like this:

Country	Capital
Zimbabwe	Harare
Poland	Poland

<?xml version=”1.0″ encoding=”ISO-8859-1″?>
<message>
<sentto>Tutor</sentto>
<sentby>Goweb99</sentby>
<subject>Tutorial</subject>
<content>This is a good tutorial!</content>
</message>

Initializing the XML Parser

We need to first initialize the XML parser in PHP, then define some handlers for different XML events, and then parse the XML file.

For eg:

<?php
//Initialize the XML parser
$parser=xml_parser_create();
//Function to use at the start of an element
function start($parser,$element_name,$element_attrs)
{
switch($element_name)
{
case “MESSAGE”:
echo “…………Message………….<br />”;
break;
case “SENTTO”:
echo “Meant for: “;
break;
case “SENTBY”:
echo “Msg From: “;

break;
case “SUBJECT”:
echo “Subject: “;
break;
case “CONTENT”:
echo “Message: “;
}
}
//Function to use at the end of an element
function stop($parser,$element_name)
{
echo “<br />”;
}
//Function to use when finding character data
function char($parser,$data)
{
echo $data;
}
//Specify element handler
xml_set_element_handler($parser,”start”,”stop”);
//Specify data handler
xml_set_character_data_handler($parser,”char”);
//Open XML file
$fp=fopen(”sample.xml”,”r”);
//Read data
while ($data=fread($filePointer,4096))
{
xml_parse($parser,$data,feof($filePointer)) or
die (sprintf(”XML Error: %s at line %d”,
xml_error_string(xml_get_error_code($parser)),
xml_get_current_line_number($parser)));
}
//Free the XML parser
xml_parser_free($parser);
?>

Output:

–Message–
Meant for:Tutor
Msg From:Goweb99
Subject: Tutorial
Message: This is a good tutorial!

The above example works as:

• Initialize the XML parser with the xml_parser_create() function
• Create functions to use with the different event handlers
• Add the xml_set_element_handler() function to specify which function will be executed when the parser encounters the opening and closing tags
• Add the xml_set_character_data_handler() function to specify which function will execute when the parser encounters character data
• Parse the file “test.xml” with the xml_parse() function
• In case of an error, add xml_error_string() function to convert an XML error to a textual description
• Call the xml_parser_free() function to release the memory allocated with the xml_parser_create() function

XML is used to describe data. It focuses on what the data is. An XML file describes the structure of the data.

In XML, no tags are predefined. You must define your own tags.

PHP can process XML files with the help of built-in XML Expat Parser.

Expat

To do the manipulation with a file we need to understand it, this is the work of a parser. Similarly to create, read, update and do other manipulations an XML document, you will need an XML parser.

There are two basic types of XML parsers:

• Tree-based parser: This parser transforms an XML document into a tree structure. It analyzes the whole document, and provides access to the tree elements. e.g. the Document Object Model (DOM)
• Event-based parser: Views an XML document as a series of events. When a specific event occurs, it calls a function to handle it. For e.g. the Expat XML parser

Event-based parsers focus on the content of the XML documents, not their structure. Because of this, event-based parsers can access data faster than tree-based parsers.

For eg:

<sent>Data</sent>

An event-based parser reports the XML above as a series of three events:

• Start element: sent
• Start CDATA section, value: Data
• Close element: from

The XML example above contains well-formed XML. However, the example is not valid XML, because there is no Document Type Definition (DTD) associated with it.

However, this makes no difference when using the Expat parser. Expat is a non-validating parser, and ignores any DTDs.

As an event-based, non-validating XML parser, Expat is fast and small, and a perfect match for PHP web applications.

Note: XML documents must be well-formed or Expat will generate an error.

If  you will not specify in which order to arrange the result, ORDER BY will arrange them in ascending order by default.

If you want to sort the records in a descending order, you can use the DESC keyword.

Syntax

SELECT column_name(s)
FROM table_name
ORDER BY column_name(s) ASC|DESC

For eg:

<?php
$conn = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
$result = mysql_query(”SELECT * FROM Country ORDER BY Country”);
while($row = mysql_fetch_array($result))
{
echo $row['Country'];
echo ” ” . $row['Capital'];
echo “<br />”;
}
mysql_close($conn);
?>

Output:

Poland Warsaw
Zimbabwe Harare

Order by Two Columns

It is also possible to order by more than one column. When ordering by more than one column, the second column is only used if the values in the first column are same:

SELECT column_name(s)
FROM table_name
ORDER BY column1, column2

Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name operator value

The following example selects all rows from the “Country” table where Country=’Poland’.

For eg:

<?php
$conn = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
$result = mysql_query(”SELECT * FROM Country
WHERE Country=’Poland’”);
while($row = mysql_fetch_array($result))
{
echo $row['Country'] . ” ” . $row['Capital'];
echo “<br />”;
}
?>

Output:

Poland Warsaw

Syntax

SELECT column_name(s)
FROM table_name

The following example selects all the data stored in the “Country” table.A * character selects all the data in the table.

For eg:

<?php
$conn = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
$result = mysql_query(”SELECT * FROM Persons”);
while($row = mysql_fetch_array($result))
{
echo $row['Country'] . ” ” . $row['Capital'];
echo “<br />”;
}
mysql_close($conn);
?>

The example above stores the data returned by the mysql_query() function in the $result variable.

Next, we use the mysql_fetch_array() function to return the first row from the recordset as an array. Each call to mysql_fetch_array() returns the next row in the recordset. The while loop loops through all the records in the recordset. To print the value of each row, we use the PHP $row variable.

Output:

Zimbabwe Harare
Poland Warsaw

Display the Result in an HTML Table

The following example selects the same data as the example above, but will display the data in an HTML table:

<?php
$conn= mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$con)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
$result = mysql_query(”SELECT * FROM Country”);
echo “<table border=’1′>
<tr>
<th>Country</th>
<th>Capital</th>
</tr>”;
while($row = mysql_fetch_array($result))
{
echo “<tr>”;
echo “<td>” . $row['Country'] . “</td>”;
echo “<td>” . $row['Capital'] . “</td>”;
echo “</tr>”;
}
echo “</table>”;
mysql_close($con);
?>

Output:

Firstname	Lastname
Zimbabwe	Harare
Poland	Warsaw

For eg:

<html>
<body>
<form action=”insert.php” method=”post”>
Country: <input type=”text” name=”country” />
Capital: <input type=”text” name=”capital” />
<input type=”submit” />
</form>
</body>
</html>

When a user clicks the submit button in the HTML form in the example above, the form data is sent to “AddValues.php”.

The “AddValues.php” file connects to a database, and retrieves the values from the form with the PHP $_POST variables.Then, the mysql_query() function executes the INSERT INTO statement, and a new record will be added to the “Country” table.

AddValues.php:

<?php
$con = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
$sql=”INSERT INTO Country (Country, Capital)
VALUES(’$_POST[country]‘,’$_POST[capital]‘)”;
if (!mysql_query($sql,$con))
{
die(’Error: ‘ . mysql_error());
}
echo “Record added successfully”;
mysql_close($conn)
?>

There are two different forms to write this statement. The first form doesn’t specify the column names where the data will be inserted, only their values:

INSERT INTO table_name VALUES (value1, value2, value3,…)

The second form specifies both the column names and the values to be inserted:

INSERT INTO table_name (column1, column2, column3,…)
VALUES (value1, value2, value3,…)

For eg:

<?php
$conn = mysql_connect(”localhost”,”tutor”,”tutor123″);
if (!$conn)
{
die(’Could not connect: ‘ . mysql_error());
}
mysql_select_db(”my_db”, $conn);
mysql_query(”INSERT INTO Persons (Country, Capital)
VALUES (’India’, ‘New Delhi’)”);
mysql_query(”INSERT INTO Persons (Country, Capital)
VALUES (’United States of America’, ‘Washington D.C.’)”);
mysql_query(”INSERT INTO Persons (Country, Capital)
VALUES (’Zimbabwe’, ‘Harare’)”);
mysql_query(”INSERT INTO Country (Country, Capital)
VALUES (’Poland’, ‘Warsaw’)”);
mysql_close($conn);
?>