(PHP 4, PHP 5)
mysql_select_db — Select a MySQL database
This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information. Alternatives to this function include:
$database_name
[, resource $link_identifier = NULL
] )Sets the current active database on the server that's associated with the specified link identifier. Every subsequent call to mysql_query() will be made on the active database.
database_nameThe name of the database that is to be selected.
link_identifierThe MySQL connection. If the
link identifier is not specified, the last link opened by
mysql_connect() is assumed. If no such link is found, it
will try to create one as if mysql_connect() was called
with no arguments. If no connection is found or established, an
E_WARNING level error is generated.
Returns TRUE on success or FALSE on failure.
Example #1 mysql_select_db() example
<?php
$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
die('Not connected : ' . mysql_error());
}
// make foo the current db
$db_selected = mysql_select_db('foo', $link);
if (!$db_selected) {
die ('Can\'t use foo : ' . mysql_error());
}
?>
Note:
For backward compatibility, the following deprecated alias may be used: mysql_selectdb()
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.
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 $db1 will actually have selected the database 'db2', because the second call to mysql_connect just returned the already opened connection ID !
You have two options here, eiher you have to call mysql_select_db before each query you do, or if you're using php4.2+ there is a parameter to mysql_connect to force the creation of a new link.
function go_mysql($query)
{
global $mysql_link;
if (!$mysql_link)
{
$mysql_link = mysql_connect("localhost","root","my_pass") or die(mysql_error());
mysql_select_db("my_db") or die(mysql_error());
mysql_query("SET NAMES 'utf8'");
mysql_query("set character_set_client='utf8'");
mysql_query("set character_set_results='utf8'");
mysql_query("set collation_connection='utf8'");
global $mysql_link;
}
$result=mysql_query($query);
if ($result)
{
return $result;
}
else
{
echo "Database Error: " . mysql_error()."<br><b>$query</b>";
die();
}
}
You can select MySQL database without using this function.
Simply right after connecting to MySQL
<?php $connection = mysql_connect("dabatbasehost", "username", "password"); ?>
perform this query:
<?php mysql_query("USE somedatabase", $connection); ?>
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);
?>
Note that the manual is slightly misleading it states :-
"Sets the current active database on the server that's associated with the specified link identifier. Every subsequent call to mysql_query() will be made on the active database."
The 2nd statement is not true or at best unclear.
mysql_query() manual entry actually correctly states it will use the last link opened by mysql_connect() by default.
Thus if you have 2 connections you will need to specify the connection when calling mysql_query or issue the connect again to ensure the 1st database becomes the default, simply using mysql_select_db will not make the 1st database the default for subsequent calls to mysql_query.
Its probably only apparent when the two databases are on different servers.
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.
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');
?>
