\(\$\)servername = "localhost";
\(\$\)username = "username";
\(\$\)password - "password";
try {
\(\$\)conn = new PDO ("mysq:host = \(\$\)servername; dbname = my DB", \(\$\)username, \(\$\)password);
//set the PDO error mode to exception
\(\$\) conn -> set Attribute (PDO:: ATTR_ERRMODE, PDO:: ERRMODE_EXCEPTION);
echo "Connected successfully";
}
catch (PDO Exception \(\$\)e)
{
echo "Connection failed; " .\(\$\)e - > get message ();
}
?>

\(\$\)servername = "localhost";
\(\$\)username ="username";
\(\$\)password = "password";
//Create connection
\(\$\)conn = mysqli ($servername, \(\$\)username, \(\$\)password);
// Check connection
if (!\(\$\)conn) {
die ("connection failed :".mysqli_connect_error());}
echo "Connected successfully";
?>

The mysqli_fetch_assoc() function fetches a result row as an associative array.
Field name returned from this function are case-sensitive.
Syntax:
Mysqli_fetch_assoc(result) ;
Here,
(i) Result set specifies that a identifier which is returned by mysqli_query(), mysqli_store_result() or mysqli_use_result( ).
(ii) It returns an associative array of strings representing the fetched row.
(iii) NULL if there are no more rows in result set.
Example:
\(\$\)con = mysqli_connect("local host", "my_user", "my_psw'", my_db");
// check connection
if ( mysqli_connect_error () )
{
echo "fail to connect to mySQL:" . mysqli_connect_error();
}
\(\$\)sqd = "SELECT Lastname, Age FROM Persons ORDER BY Lastname";
\(\$\)result = mysqli-query(\(\$\)con, \(\$\)sql) ;
// Associative array
\(\$\) row = mysqli_fetch-assoc (\(\$\) result);
printf ("%s (%s) \n", \(\$\)row ["last name"], \(\$\)row ["Age"]);
//free result set
mysqli_free_result ($ result) ;
mysqli_close ($con);
?>

MySQL is a database system used on the web.
(i) It is a database system that runs on a server.
(ii) It is ideal for both small and large applications.
(iii) It is very fast, reliable and easy to use.
(iv) It uses standard SQL.
(v) It compiles on a member of platforms.
(vi) It is free to download and use.
(vii) It is developed, distributed and supported by Oracle Corporation.
(viii) It is named after co-founder Monty Widenius's daughter.
(ix) The data in a MySQL database are stored in tables.
(x) A table is a collection of related data, and it consists of columns & rows.
(xi) Databases are useful for storing information categorically.

(i) Four Parameters are used to connect to the Database server.
(ii) They are
1.＄ servername -> Database Server server IP address
2.＄ susername -> Database Server User Name
3.＄ password -> Database Server Password
4.＄ DB_Name -> Database Name

Error handling is the process of catching errors raised by our program and then taking appropriate action.
Different error handling methods are
Simple "die ()" statements;
Custom error and error triggers;
Error reporting.
(i) Using the die () function:-
Example:
$file = fopen("Welcome.txt", "r");
?>
Above example shows a simple script that opens a text file. If the file does not exists you might get an error like this.
Warning:
fopen (welcome.txt) [function.fopen]: failed to open stream: No such file or directory in
C:\webfolder\test.php on line 2
To prevent the user from getting an error message like the one above, test whether the file before we
try to access it.
if (!file_exists ("welcome.txt"))
{
die ("File not found");
} else
{
file = fopen ("Welcome.txt", "r");
}
Now if the file does not exists you get an error like this
File not found
The code above is more efficient than the earlier code, because it uses a simple error handling mechanism to stop the script after the error.
However, simply stopping the script is not always the right way to go. Let's take a look at alternative php functions for handling errors.
(ii) Creating a custom Error Handler
Creating a custom error handler is quite simple. Simply create a special function that can be called when an error occurs in PHP.
This function must be able to handle a minimum of two parameters (error level and error message) but can accept up to five parameters.
Syntax:
error_function (error_level, error_message, error_file, error_line, error_context)
(iii) Error report levels:
These error report levels are the different types of error the user defined error handler can be used for:
E_WARNING, E_NOTICE, E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE,... etc.
Set Error Handler:
The default error handling for PHP is the built-in error handle;
Example:
To use our custom error handle for all errors:
set_error_handler("Custom Error");