PHP & MySQL - Select Database

Once a connection with a database server is established, it may be required to select a particular database. This is required because a database server may contain multiple databases and you can work with a single database at a time.

Along with this, to connect to the MySQL server, mysqli_connect() function can be used. After establishing the connection, mysql_select_db() function can be used to select the default database to be used when performing queries against the database connection.

Select a MySQL Database - Object-oriented style

The example below demonstrates how to select the default database in object-oriented style.

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDb1";

//establishing connection 
$mysqli = new mysqli($servername, $username, $password, $dbname);

//checking connection
if ($mysqli->connect_errno) {
  echo "Failed to connect to MySQL: ". $mysqli->connect_error;
  exit();
}

//getting the name of the current default database
$result = $mysqli->query("SELECT DATABASE()");
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);

//changing default database to "myDb2"
$mysqli->select_db("myDb2");

//getting the name of the current default database
$result = $mysqli->query("SELECT DATABASE()");
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);

//closing the connection
$mysqli->close();
?>

The output of the above code will be:

Default database is myDb1.
Default database is myDb2.

Select a MySQL Database - Procedural style

To obtain the same result using procedural style, the following script can be used.

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDb1";

//establishing connection 
$mysqli = mysqli_connect($servername, $username, $password, $dbname);

//checking connection
if (mysqli_connect_errno()) {
  echo "Failed to connect to MySQL: ". mysqli_connect_error();
  exit();
}

//getting the name of the current default database
$result = mysqli_query($mysqli, "SELECT DATABASE()");
$row = mysqli_fetch_row($result);
printf("Default database is %s.\n", $row[0]);

//changing default database to "myDb2"
mysqli_select_db($mysqli, "myDb2");

//getting the name of the current default database
$result = $mysqli->query("SELECT DATABASE()");
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);

//closing the connection
mysqli_close($mysqli);
?>

The output of the above code will be:

Default database is myDb1.
Default database is myDb2.

Complete PHP MySQLi Reference

For a complete reference of all properties, methods and functions of PHP MySQLi extension, see PHP MySQLi Reference.