PHP has several built-in functions for connecting to and manipulating MySQL databases, including mysqli_connect() to establish a connection, mysqli_select_db() to select a database, mysqli_query() to execute SQL queries, mysqli_num_rows() to get the number of rows returned from a select query, mysqli_fetch_array() to fetch row arrays from query results, and mysqli_close() to close an open database connection. Each function has a defined syntax using parameters like the database connection handler and query string.

1. PHP has a rich collection of built in functions for manipulating MySQL
databases.
PHP mysqli_connect function:
The PHP mysql connect function is used to connect to a MySQL database
server. mysql_connect function have three parameters servername, user and
password.
It has the following syntax:
<?php;
$db_handle = mysqli_connect($server_name,
$user_name, $password)
?>
 “$db_handle” is the database connection resource variable.
 “mysqli_connect(…)” is the function for php database connection
 “$server_name” is the name or IP address of the server hosting
MySQL server.
 “$user_name” is a valid user name in MySQL server.
 “$password” is a valid password associated with a user name in
MySQL server.
PHP mysqli_select_db function:
The mysqli_select_db function is used to select a database.
It has the following syntax:
<?php
mysqli_select_db($db_handle,$database_name);
?>
 “mysqli_select_db(…)” is the database selection function that returns
either true or false
 “$db_handle” is optional, it is used to pass in the server connection
link
 “$database_name” is the name of the database
PHP mysqli_query function:

2. The mysqli_query function is used to execute SQL queries. The function can
be used to execute the following query types;
Insert, Select, Update and delete statements.
It has the following syntax:
<?php
mysqli_query($db_handle,$query);
?>
PHP mysqli_num_rows function:
The mysqli_num_rows function is used to get the number of rows returned
from a select query.
It has the following syntax:
<?php
mysqli_num_rows($result);
?>
 “mysqli_num_rows(…)” is the row count function
 “$result” is the mysqli_query result set
PHP mysqli_fetch_array function:
The mysqli_fetch_array function is used fetch row arrays from a query result
set.
It has the following syntax:
<?php
mysqli_fetch_array($result);
?>
PHP mysqli_close function:
The mysqli_close function is used to close an open database connection.
It has the following syntax:
<?php
mysqli_close($db_handle);
?>