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    mysql_select_db

    (PHP 4, PHP 5)

    mysql_select_db — MySQL データベースを選択する

    警告

    この拡張モジュールは PHP 5.5.0 で非推奨になり、PHP 7.0.0 で削除されました。 MySQLi あるいは PDO_MySQL を使うべきです。詳細な情報は MySQL: API の選択 を参照ください。 この関数の代替として、これらが使えます。

    説明

    mysql_select_db(string $database_name, resource $link_identifier = NULL): bool

    指定したリンク ID が指すサーバー上のデータベースを、アクティブな データベースに設定します。それ以降にコールされる mysql_query() は、すべてアクティブなデータベース上で 実行されます。

    パラメータ

    database_name

    選択するデータベース名。

    link_identifier

    MySQL 接続。指定されない場合、mysql_connect() により直近にオープンされたリンクが指定されたと仮定されます。そのようなリンクがない場合、引数を指定せずに mysql_connect() がコールした時と同様にリンクを確立します。リンクが見付からない、または、確立できない場合、E_WARNING レベルのエラーが生成されます。

    戻り値

    成功した場合に true を、失敗した場合に false を返します。

    例

    例1 mysql_select_db() の例

    <?php

    $link     = mysql_connect('localhost', 'mysql_user', 'mysql_password');
    if (!    $link) {
    die(    'Not connected : ' . mysql_error());
    }

    // foo をカレントの db に指定する
    $db_selected = mysql_select_db('foo', $link);
    if (!    $db_selected) {
    die (    'Can\'t use foo : ' . mysql_error());
    }
    ?>

    注意

    注意:

    下位互換のために、次の非推奨別名を使用してもいいでしょう。 mysql_selectdb()

    参考

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    User Contributed Notes 6 notes

    up
    10
    james at gogo dot co dot nz
    20 years ago
    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.
    up
    -2
    Maarten
    19 years ago
    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.
    up
    -22
    anotheruser at example dot com
    16 years ago
    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);

    ?>
    up
    -31
    duncan at berrimans dot co dot uk
    12 years ago
    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.
    up
    -33
    miloshio at gmail dot com
    12 years ago
    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); ?>
    up
    -41
    me at khurshid dot com
    17 years ago
    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.
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