mysql_select_db

(PHP 4, PHP 5)

mysql_select_db — Sélectionne une base de données MySQL

Description

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

Sélectionne une base de données MySQL sur le serveur associé avec le paramètre link_identifier . Chaque appel à la fonction mysql_query() sera exécutée sur la base de données active.

Liste de paramètres

database_name: Le nom de la base de données à sélectionner.
link_identifier: La connexion MySQL. S'il n'est pas spécifié, la dernière connexion ouverte avec la fonction mysql_connect() sera utilisée. Si une telle connexion n'est pas trouvée, la fonction tentera d'ouvrir une connexion, comme si la fonction mysql_connect() avait été appelée sans argument. Si aucune connexion n'est trouvée ou établie, une alerte E_WARNING est générée.

Valeurs de retour

Cette fonction retourne TRUE en cas de succès, FALSE en cas d'échec.

Exemples

Exemple #1 Exemple avec mysql_select_db()


<?php

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
   die('Impossible de se connecter : ' . mysql_error());
}

// Rendre la base de données foo, la base courante
$db_selected = mysql_select_db('foo', $link);
if (!$db_selected) {
   die ('Impossible de sélectionner la base de données : ' . mysql_error());
}
?>

Notes

Note: Pour des raisons de compatibilité ascendante, l'alias obsolète suivant peut être utilisé : mysql_selectdb()

Voir aussi

mysql_connect() - Ouvre une connexion à un serveur MySQL
mysql_pconnect() - Ouvre une connexion persistante à un serveur MySQL
mysql_query() - Envoie une requête à un serveur MySQL

mysql_set_charset

mysql_result

Last updated: Fri, 14 Aug 2009

add a note User Contributed Notes
mysql_select_db

riad93 at mail dot ru
12-Sep-2009 08:44


You can use DataBases without <?php mysql_select_db() ?>



And you will havenot james at gogo dot co dot nz's problems :)



<?php

mysql_connect('localhost','db_user','pssword');

mysql_query('SELECT * FROM database_name.table_name');



?>

anotheruser at example dot com
13-Aug-2008 08:57


Cross-database join queries, expanding on Dan Ross's post...



Really, this is a mysql specific feature, but worth noting here.  So long as the mysql user has been given the right permissions to all databases and tables where data is pulled from or pushed to, this will work.  Though the mysql_select_db function selects one database, the mysql statement may reference another (the syntax for referencing a field in another db table being 'database.table.field').



<?php



$sql_statement = "SELECT

    PostID,

    AuthorID,

    Users.tblUsers.Username

    FROM tblPosts

    LEFT JOIN Users.tblUsers ON AuthorID = Users.tblUsers.UserID

    GROUP BY PostID,AuthorID,Username

    ";



$dblink = mysql_connect("somehost", "someuser", "password");

mysql_select_db("BlogPosts",$dblink);

$qry = mysql_query($sql_statement,$dblink);



?>

me at khurshid dot com
09-Sep-2007 03:03


Problem with connecting to multiple databases within the same server is that every time you do:

mysql_connect(host, username, passwd);

it will reuse 'Resource id' for every connection, which means you will end with only one connection reference to avoid that do:

mysql_connect(host, username, passwd, true);

keeps all connections separate.

Maarten
19-Aug-2005 09:09


About opening connections if the same parameters to mysql_connect() are used: this 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 09:39


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...

james at gogo dot co dot nz
17-Jan-2004 09:45


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
18-Dec-2003 05:39


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".





<?php


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'");


?>

add a note

mysql_set_charset

mysql_result

Last updated: Fri, 14 Aug 2009