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    mysql_unbuffered_query

    (PHP 4 >= 4.0.6, PHP 5)

    mysql_unbuffered_query — Send an SQL query to MySQL without fetching and buffering the result rows

    Avviso

    Questa enstensione deprecata da PHP 5.5.0, e sarà rimossa in futuro. Al suo posto, usare l'estensione MySQLi o PDO_MySQL. Vedere anche la guida MySQL: scelta dell'API e le FAQ relative per ulteriori informazioni. Le alternative a questa funzione includono:

    Descrizione

    mysql_unbuffered_query(string $query, resource $link_identifier = NULL): resource

    mysql_unbuffered_query() sends the SQL query query to MySQL without automatically fetching and buffering the result rows as mysql_query() does. This saves a considerable amount of memory with SQL queries that produce large result sets, and you can start working on the result set immediately after the first row has been retrieved as you don't have to wait until the complete SQL query has been performed. To use mysql_unbuffered_query() while multiple database connections are open, you must specify the optional parameter link_identifier to identify which connection you want to use.

    Elenco dei parametri

    query

    The SQL query to execute.

    Data inside the query should be properly escaped.

    link_identifier

    La connessione MySQL. Se l'identificativo di connessione non è specificato, l'ultima connessione aperta da mysql_connect() viene assunta. Se questa connessione non è trovata, si cercherà di crearne una come se mysql_connect() fosse stata chiamata senza argomenti. Se una connessione non è trovata oppure non viene stabilita, un avviso di livello E_WARNING viene generato.

    Valori restituiti

    For SELECT, SHOW, DESCRIBE or EXPLAIN statements, mysql_unbuffered_query() returns a resource on success, or false on error.

    For other type of SQL statements, UPDATE, DELETE, DROP, etc, mysql_unbuffered_query() returns true on success or false on error.

    Note

    Nota:

    The benefits of mysql_unbuffered_query() come at a cost: you cannot use mysql_num_rows() and mysql_data_seek() on a result set returned from mysql_unbuffered_query(), until all rows are fetched. You also have to fetch all result rows from an unbuffered SQL query before you can send a new SQL query to MySQL, using the same link_identifier.

    Vedere anche:

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    User Contributed Notes 5 notes

    up
    3
    frappyjohn at dos2linux dot org
    21 years ago
    Don't let the two hands confuse you, these are both advantages (they should really be on the same hand):

    On the one hand, this saves a considerable amount of memory with SQL queries that produce large result sets.

    On the other hand, you can start working on the result set immediately ...
    up
    2
    crazyone at crazycoders dot net
    16 years ago
    You are NOT required to read all rows from the resultset when using unbuffered query, you may opt out at any time and use mysql_free_result. Imagine looking at 1 million row when the first 50 suffice? Just free the result and you are good to go again.
    up
    0
    post at jfl dot dk
    20 years ago
    If using optimized MyISAM tables I guess there is a big advantage with this function as it is possible to do selects and inserts on the same time as long as no rows in the table gets updated.
    up
    -13
    shaner at accretivetg dot com
    21 years ago
    Regarding bailing on a really large result, while doing an unbuffered query, there _is_ a way to do this: kill the thread and exit your processing loop.  This, of course, requires having a separate database link.  Something like below does the trick:

    <?php
    // a db link for queries
    $lh  = mysql_connect( 'server', 'uname', 'pword' );
    // and a controller link
    $clh = mysql_connect( 'server', 'uname', 'pword', true );

    if (     mysql_select_db ( 'big_database', $lh ) )
    {
          $began  =  time();
          $tout   = 60 * 5; // five minute limit
          $qry    = "SELECT * FROM my_bigass_table";
          $rh     = mysql_unbuffered_query( $qry, $lh );
          $thread = mysql_thread_id ( $lh );
      while (     $res = mysql_fetch_row( $rh ) )
      {
            /* do what you need to do
         * ...
         * ...
         */
            if ( ( time() - $began ) > $tout )
        {
              // this is taking too long
              mysql_query( "KILL $thread", $clh );
          break;
        }
      }
    }
    ?>
    up
    -9
    david at php dot net
    22 years ago
    You are absolutely required to retrieve all rows in the result set (option 'a' in the first comment). If you fail to do so, PHP will do so for you, and will emit a NOTICE warning you of the fact. From the MySQL API, "Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for. ".

    Also note that if you are using this function, you should be quick about processing the result set, or you will tie up the MySQL server (other threads will be unable to write to the tables you are reading from).

    If you want to be able to 'abort' mid result-set or if you want to do lengthy processing on the results, you are misunderstanding the purpose of this function.

    Also note that UPDATE queries etc return no result set, so this function is only useful for SELECT etc.
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