(PHP 5, PHP 7)
mysqli::select_db -- mysqli_select_db — Selects the default database for database queries
Object oriented style
$dbname
)Procedural style
Selects the default database to be used when performing queries against the database connection.
Note:
This function should only be used to change the default database for the connection. You can select the default database with 4th parameter in mysqli_connect().
linkProcedural style only: A link identifier returned by mysqli_connect() or mysqli_init()
dbnameThe database name.
Returns TRUE on success or FALSE on failure.
Example #1 mysqli::select_db() example
Object oriented style
<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "test");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
/* return name of current default database */
if ($result = $mysqli->query("SELECT DATABASE()")) {
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);
$result->close();
}
/* change db to world db */
$mysqli->select_db("world");
/* return name of current default database */
if ($result = $mysqli->query("SELECT DATABASE()")) {
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);
$result->close();
}
$mysqli->close();
?>
Procedural style
<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "test");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
/* return name of current default database */
if ($result = mysqli_query($link, "SELECT DATABASE()")) {
$row = mysqli_fetch_row($result);
printf("Default database is %s.\n", $row[0]);
mysqli_free_result($result);
}
/* change db to world db */
mysqli_select_db($link, "world");
/* return name of current default database */
if ($result = mysqli_query($link, "SELECT DATABASE()")) {
$row = mysqli_fetch_row($result);
printf("Default database is %s.\n", $row[0]);
mysqli_free_result($result);
}
mysqli_close($link);
?>
The above examples will output:
Default database is test. Default database is world.
If you are on a shared server and you get the following response from your script:
Fatal error: Call to undefined function: mysqli_connect()
this mean the version of PHP your web host is using does not support mysqli or mysqli is not enabled in PHP.
In some situations its useful to use this function for changing databases in general. We've tested it in production environment and it seams to be faster with switching databases than creating new connections.
Note that in the second example, if the database "world" does not exist, the database selected does not change. You may need to add additional code to ensure that you are connected to the correct database.
