The mysqli_connect-errno ( ) function returns the error description from the last connection error, if any.
Syntax
mysql_connect_error();
It returns a string that describes the error. NULL if no error occurred.
Example:
\(\$\)conn = mysqli_connect('local host","wrong_user", "my_psw", "my_db");
// Check connection
if (!\(\$\)conn) {die("Connection error: " . mysqli_connect_errno());
}
?>

Mysqli_affected_rows ( ) function returns the number of affected rows in the previous SELECT INSERT, UPDATE, REPLACE or DELETE query.
Syntax
mysqli_affected_rows(connection);
Here,
(i) a Connection specifies the MySQL connection to use.
(ii) It returns value which is integer > 0 indicates the number of rows affected.
'0' indicates that no records were affected.
'-1' indicates that the query returned an error.

Mysqli_select_db() function is used to change the default database for the connection. It returns TRUE value to success or FALSE value on failure.
Syntax:
mysqli_select_db(connection, db narne);
where,
(i) Connection - specifies the Mysql connection to use
(ii) db name - specifies the default database to be used.

(i) PHP is the most popular scripting language for web development It is free, open-source and server-side.
(ii) MySQL is a Relational Database Management System (RDBMS) that uses Structured Query Language (SQL).

1. PHP provides various functions to access the MySQL database and to manipulate the data records inside the MySQL database.
2. We require to call the PHP functions in the same way we call any other PHP function.
General format for PHP functions use with MySQL
Mysql_function(value, value...)

(i) The mysqll_connect function uses these variables and connect Database server from PHP scripting.
 (ii) If connection gets fail, output will be printed with MySQL error code. Otherwise connection is success.

The SQL query statements are helping with PHP MySQL extension to achieve the objective of MySQL and PHP connection.

The main goal of MySQL and PHP connectivity is to retrieve and manipulate the data from MySQL database server.

(i) MySQL is the most popular Open Source Relational SQL Database Management System.
(ii) MySQL is one of the best RDBMS being used for developing various web-based software applications.

Database Connections: Accessing MySQL Database, connect to Database Server machine via PHP scripting language using Mysqli_connect() Function.
Syntax:
mysqli_connect("Server Name","User Name","Password","DB Name");
This function requires four parameters to connect to database server. Database Server name, Database username, password and Database Name.