mysql_select_db

(PHP 4, PHP 5)

mysql_select_db — Auswahl einer MySQL Datenbank

Beschreibung

bool mysql_select_db ( string $database_name [, resource $link_identifier ] )

Setzt die aktive Datenbank auf dem Server die mit der angegebenen Verbindung assoziiert ist. Jeder nachfolgende Aufruf von mysql_query() operiert auf dieser aktiven Datenbank.

Parameter-Liste

database_name: Der Name der zu selektierenden Datenbank.
Verbindungs-Kennung: Die MySQL-Verbindung. Wird die Verbindungskennung nicht angegeben, wird die letzte durch mysql_connect() geöffnete Verbindung angenommen. Falls keine solche Verbindung gefunden wird, wird versucht, eine Verbindung aufzubauen, wie es beim Aufruf von mysql_connect() ohne Angabe von Argumenten der Fall wäre. Falls zufällig keine Verbindung gefunden oder aufgebaut werden kann, wird eine Warnung der Stufe E_WARNING erzeugt.

Rückgabewerte

Gibt bei Erfolg TRUE zurück. Im Fehlerfall wird FALSE zurückgegeben.

Beispiele

Beispiel #1 mysql_select_db() Beispiel


<?php

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
    die('Verbindung nicht möglich : ' . mysql_error());
}

// benutze Datenbank foo
$db_selected = mysql_select_db('foo', $link);
if (!$db_selected) {
    die ('Kann foo nicht benutzen : ' . mysql_error());
}
?>

Anmerkungen

Hinweis:
Für die Abwärtskompatibiliät kann der folgende veraltete Alias verwendet werden: mysql_selectdb()

Siehe auch

mysql_connect() - Öffnet eine Verbindung zu einem MySQL-Server
mysql_pconnect() - Öffnet eine persistente Verbindung zum MySQL Server
mysql_query() - Sendet eine Anfrage an MySQL

add a note User Contributed Notes
mysql_select_db

matsko at rogers dot com
10-May-2006 09:19


Just incase the mysql_select_db() function still won't work with multiple database connections (as has happened to me before).



$dbh1 = mysql_pconnect($host,$user,$pass);

$dbh2 = mysql_pconnect($host,$user,$pass);



You could do this...



mysql_query("USE database1",$dbh1);

mysql_query("Use database2",$dbh2);



This does the same thing as the mysql_select_db() function...



or this...



You don't even have to select the database for each connection.



mysql_query("SELECT * FROM database1.table",$dbh1);

mysql_query("SELECT * FROM database2.table",$dbh2);

Maarten
19-Aug-2005 02:09


Previously posted comments about opening connections if the same parameters to mysql_connect() are used can be avoided by using the 'new_link' parameter to that function.



This parameter has been available since PHP 4.2.0 and allows you to open a new link even if the call uses the same parameters.

buzz at oska dot com
06-May-2005 02:39


As has been already commented, opening multiple connection handles with:

<?php 

$connection_handle =  mysql_connect($hostname_and_port,$user,$password);

?>

causes the connection ID/handle to be REUSED if the exact same parameters are passed in to it.   This can be annoying if you want to work with multiple databases on the same server, but don't want to (a) use the database.table syntax in all your queries or (b) call the mysql_select_db($database) before every SQL query just to be sure which database you are working with.     

My solution is to create a handle for each database with mysql_connect (using ever so slightly different connection properties), and assign each of them to their own database permanently.  each time I do a mysql_query(...) call, I just include the connection handle that I want to do this call on eg (ive left out all error checking for simplicity sake):

<?php

// none of thesehandles are re-used as the connection parameters are different on them all, despite connecting to the same server (assuming 'myuser' and 'otheruser' have the same privileges/accesses in mysql)

$handle_db1 = mysql_connect("localhost","myuser","apasswd");

$handle_db2 = mysql_connect("127.0.0.1","myuser","apasswd");

$handle_db3 = mysql_connect("localhost:3306","myuser","apasswd");

$handle_db4 = mysql_connect("localhost","otheruser","apasswd");



// give each handle it's own database to work with, permanently.

mysql_select_db("db1",$handle_db1);

mysql_select_db("db2",$handle_db2);

mysql_select_db("db3",$handle_db3);

mysql_select_db("db4",$handle_db4);



//do a query from db1:

$query = "select * from test"; $which = $handle_db1;

mysql_query($query,$which);



//do a query from db2 :

$query = "select * from test"; $which = $handle_db2;

mysql_query($query,$which);



//etc 

?>



Note that we didn't do a mysql_select_db between queries , and we didn't use the database name in the query either.



Of course, it has the overhead of setting up an extra connection.... but you may find this is preferable in some cases...

Dan Ross
12-Feb-2004 10:43


Another way to select from 2 different databases on the same server:



mysql_select_db("db1");



$res_db1 = mysql_query("select * from db1.foobar");

$res_db2 = mysql_query("select * from db2.foobar");



I.e. just prepend database name.

james at gogo dot co dot nz
17-Jan-2004 01:45


Be carefull if you are using two databases on the same server at the same time.  By default mysql_connect returns the same connection ID for multiple calls with the same server parameters, which means if you do 



<?php

  $db1 = mysql_connect(...stuff...);

  $db2 = mysql_connect(...stuff...);

  mysql_select_db('db1', $db1);

  mysql_select_db('db2', $db2); 

?>



then $db1 will actually have selected the database 'db2', because the second call to mysql_connect just returned the already opened connection ID !



You have two options here, eiher you have to call mysql_select_db before each query you do, or if you're using php4.2+ there is a parameter to mysql_connect to force the creation of a new link.

doug at xamo dot com
17-Dec-2003 09:39


When you need to query data from multiple databases, note that mysql_select_db("db2")  doesn't prevent you from fetching more rows with result sets returned from "db1".



mysql_select_db("db1");



$res_db1=mysql_query("select * from foobar");



myqsl_select_db("db2);



$row_db1=mysql_fetch_object($res_db1);



$res_db2=mysql_query("select * from test where id='$row_db1->id'");

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Last updated: Fri, 18 May 2012