8 Tips for PHP and MySQL Development_PHP Tutorial

For websites with LAMP architecture, I used to focus mostly on the installation/configuration aspect, and I rarely talked about development because I rarely engaged in development myself. The original text of this article is of course also from:

Published on The OReilly Network (http://www.oreillynet.com/)
http://www.oreillynet.com/pub/a/onlamp/2002/04/04/webdb.html

After reading it, I was quite inspired. Some of the problems encountered in previous development were easily solved. So I translated it and shared it with everyone.

1. The use of arrays in PHP
When operating a database, it is very helpful to use associatively-indexed arrays. Let’s look at a basic array traversal in digital format:

$temp[0] = "richmond";
$temp[1] = "tigers";
$temp[2] = "premiers";

for($x=0;$x
{
echo $temp[$x];
echo " ";
}
?>

However, another way to save code is:

$temp = array("richmond", "tigers", "premiers");
foreach ($temp as $element)
echo "$element ";
?>

foreach can also output text subscripts:

$temp = array("club" => "richmond",
"nickname" =>"tigers",
"aim" => "premiers");

foreach ($temp as $key => $value)
echo "$key : $value ";
?>
The PHP manual describes about 50 methods for working with arrays function.

2. Add variables to PHP strings

This is very simple:
$temp = "hello"
echo "$temp world";
?>

But it should be noted that although the following example has no error:
$temp = array("one" => 1, "two" => 2);
// Output:: The first element is 1
echo "The first element is $temp[one].";
?>

But if the following echo statement is not enclosed in double quotes, an error will be reported, so it is recommended to use curly braces:

$temp = array("one" => 1, "two" => 2);
echo "The first element is {$temp["one"]}.";
? >

3. Use associative array to access query results
Look at the following example:

$connection = mysql_connect("localhost", "albert", "shhh");
mysql_select_db("winestore", $connection);

$result = mysql_query("SELECT cust_id, surname,
firstname FROM customer", $connection);

while ($row = mysql_fetch_array($result))
{
echo "ID: {$row["cust_id"]} ";
echo "Surname {$row["surname"]} ";
echo "First name: {$row["firstname"]} ";
}
?>

The function mysql_fetch_array() puts a row of the query result into an array, which can be referenced in two ways at the same time. For example, cust_id can be referenced in the following two ways at the same time: $row["cust_id"] or $row[0]. Obviously, the former is much more readable than the latter.

In multi-table continuous query, if two columns have the same name, it is best to separate them with aliases:

SELECT winery.name AS wname,
region.name AS rname,
FROM winery, region
WHERE winery.region_id = region.region_id;

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The reference of the column name is: $row["wname"] and $row["rname"].

When table and column names are specified, only the column names are quoted:

SELECT winery.region_id
FROM winery

The reference to the column name is: $row["region_id"].

The reference of the aggregate function is the reference name:

SELECT count(*)
FROM customer;

The reference of the column name is: $row["count(*)"].

4. Pay attention to common PHP bugs
Common PHP debugging problems are:

No page rendered by the Web browser when much more is expected
A pop-up dialog stating that the "Document Contains No Data"
A partial page when more is expected

Most of the reasons for these situations are not the logic of the script, but bugs in the HTML or bugs in the HTML generated by the script. For example, if a closing tag like , is missing, the page cannot be refreshed. The solution to this problem is to look at the source code of the HTML.

For complex pages whose reasons cannot be found, you can analyze them through the W3C page validation program http://validator.w3.org/.

If the variable is not defined, or the variable definition is wrong, the program will become weird. For example, the following infinite loop:

for($counter=0; $counter<10; $Counter++)
myFunction();
?>

The variable $Counter is increasing, but $counter is always less than 10. This type of error can generally be found by setting a higher error reporting level:

error_reporting(E_ALL);

for($counter=0; $counter<10; $Counter++)
myFunction();
?>

5. Use the header() function to process single-part queries

In many web database applications, some functions often allow users to continue to stay on the current page after clicking a link. I call this kind of work "single component query".

The following is a script called calling.php:

"-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/ html4/loose.dtd" >

Click here!

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When the user clicks on the link above, action.php is called. The following is the source code of action.php:

// Database function

// Redirect
header("Location: $HTTP_REFERER");
exit;
?>

There are two common mistakes that need to be reminded here:
After calling the header() function, you must include an exit statement to stop the script, otherwise subsequent scripts may be output before the header is sent.

A common mistake in the header() function is:

Warning: Cannot add header information - headers already sent...

The header() function can only be called before HTML output, so you need to check for possible empty lines, spaces, etc. in front of php.

6. Reload problem and its solution
When I used to write PHP programs, I often encountered the situation where the database processed it one more time when the page was refreshed.
Let’s take a look at addcust.php:

$query = "INSERT INTO customer
SET surname = $surname,
firstname = $firstname";
$connection = mysql_connect("localhost", "fred", "shhh");
mysql_select_db("winestore", $connection);
$result = mysql_query($query, $connection);
?>

"-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd" >

Ive inserted the customer for you.

?>
Suppose we use this program with the following connection:

http://www.freelamp.com/addcust.php?surname=Smith&firstname=Fred

If this request is submitted only once, OK, there will be no problem, but if you refresh it multiple times, you will insert multiple records.
This problem can be solved through the header() function: Here is the new version of addcust.php:

$query = "INSERT INTO customer
SET surname = $surname,
firstname = $firstname";
$connection = mysql_connect("localhost", "fred", "shhh");
mysql_select_db("winestore", $connection);
$result = mysql_query($query, $connection);
header("Location: cust_receipt.php");
?>
This script redirects the browser to a new page: cust_receipt.php:

"-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd" >

Ive inserted the customer for you.

In this way, there will be no side effects if the original page continues to be refreshed.

7. Use the lock mechanism skillfully to improve application performance
If we want to run a report urgently, then we can add a write lock to the table to prevent others from reading and writing, so as to increase the processing speed of the table.

8. Use mysql_unbuffered_query() to develop fast scripts
This function can be used to replace the mysql_query() function. The main difference is that mysql_unbuffered_query() returns immediately after executing the query, without waiting or locking the database.

But the number of rows returned cannot be checked with the mysql_num_rows() function because the size of the output result set is unknown.

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