PHP 7.2.0 Release Candidate 2 Released


(PHP 4 >= 4.0.6, PHP 5)

mysql_unbuffered_query Invia una query SQL a MySQL senza caricare e bufferare le righe risultanti


resource mysql_unbuffered_query ( string $query [, resource $identificativo_connessione [, int $modo_risultato ]] )

mysql_unbuffered_query() invia una query SQL query a MySQL senza caricare e bufferare le righe risultanti automaticamente come fa mysql_query(). Da una parte, questo risparmia un considerevole quantità di memoria con le query SQL che producono risulati di grandi dimensioni. Dall'altra parte, si può iniziare l'elaborazione dei risultati immediatamente dopo che la prima riga è stata recuperata: non si deve attendere finché la query SQL sia completamente eseguita. Quando si usano diverse connessioni a database, si deve specificare il paramentro opzionale identificativo_connessione.

Il parametro opzionale modo_risultato può essere MYSQL_USE_RESULT e MYSQL_STORE_RESULT. Il valore predefinito è MYSQL_USE_RESULT, quindi il risultato non è bufferato. Vedere anche mysql_query() per la controparte di questo comportamento.


I benefici di mysql_unbuffered_query() hanno un costo: non si può usare mysql_num_rows() su un risultato restituito da mysql_unbuffered_query(). Inoltre si debbono caricare tutte le righe risultanti da una query SQL non bufferata prima di poter inviare una nuova query SQL a MySQL.

vedere anche: mysql_query().

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User Contributed Notes 5 notes

frappyjohn at dos2linux dot org
14 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 ...
crazyone at crazycoders dot net
9 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.
post at jfl dot dk
13 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.
shaner at accretivetg dot com
14 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:

// 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 );
david at php dot net
15 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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