Fonctions MySQL
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.
mysql_unbuffered_query
(PHP 4 >= 4.0.6, PHP 5, PECL mysql:1.0)
mysql_unbuffered_query — Exécute une requête SQL sans mobiliser les résultats MySQL
Description
resource mysql_unbuffered_query
( string $query
[, resource $link_identifier
] )
mysql_unbuffered_query() envoie la requête SQL query au serveur MySQL identifié par link_identifier , sans préparer les résultats pour la lecture, comme le fait mysql_query(). D'une part, cela réduit considérablement la consommation de mémoire par MySQL, lorsque les requêtes génèrent des résultats de grande taille. D'autre part, vous pourrez utiliser les résultats dès que la première ligne aura été lue : pas besoin d'attendre que la requête ait complètement été exécutée. Lorsque vous utilisez de multiples connexions à MySQL, vous devez spécifier le paramètre optionnel link_identifier .
Liste de paramètres
- query
-
Une requête SQL
- 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
Pour les requêtes SELECT, SHOW, DESCRIBE ou EXPLAIN, mysql_unbuffered_query() retourne une ressource en cas de succès, ou FALSE si une erreur survient.
Pour les autres types de requêtes, UPDATE, DELETE, DROP, etc, mysql_unbuffered_query() retourne TRUE en cas de succès ou FALSE si une erreur survient.
Notes
Note: L'intérêt de mysql_unbuffered_query() est tempéré par une limitation : mysql_num_rows() et mysql_data_seek() ne fonctionne pas sur une ressource retournée par mysql_unbuffered_query(). Vous devez aussi lire tous les résultats d'une première requête exécutée avec mysql_unbuffered_query(), avant de pouvoir en exécuter une autre.
add a note
User Contributed Notesmysql_unbuffered_query
crazyone at crazycoders dot net
27-May-2008 06:47
27-May-2008 06:47
Typer85 at gmail dot com
28-Dec-2006 01:33
28-Dec-2006 01:33
In response to "silvanojr at gmail dot com".
Your misunderstanding the point of this function. You MUST retrieve all rows in the result set BEFORE you issue another query.
Yes you can do a SQL_CALC_ROWS but that would mean you would have to query MySQL, thus either firing an error or deleting the previous query's result set as the new unbuffered result set would point to the result of the call to SQL_CALC_ROWS.
Keep that in mind folks,
silvanojr at gmail dot com
12-May-2006 11:02
12-May-2006 11:02
Note: The benefits of mysql_unbuffered_query() come at a cost: You cannot use mysql_num_rows() and...
but it looks like you can use SQL_CALC_ROWS on MySQL to get the total rows without the limit.
andre dot steffens at adress-research dot de
08-Oct-2004 03:18
08-Oct-2004 03:18
If you use mysql_ping() to check the connection, the resultset from mysql_unbuffered_query() will be kill.
steve_stockman at mac dot symantec dot com
02-Apr-2004 12:19
02-Apr-2004 12:19
If you are going to do a large query, but are concerned about blocking access to the table during an unbuffered query, why not go through a temporary table? (Of course, this is predicated on the current user having permission to create tables.)
$dbQuery = "SELECT something ...";
if (mysql_query ("CREATE TEMPORARY TABLE MyQuery $dbQuery")) {
$numRows = mysql_affected_rows();
if ($numRows == 0) {
/* handle empty selection */
} else {
$result = mysql_unbuffered_query ('SELECT * FROM MyQuery');
/* handle result */
}
mysql_query ('DROP TABLE MyQuery');
}
post at jfl dot dk
30-Nov-2003 02:57
30-Nov-2003 02:57
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.
14-Jun-2003 07:35
The other hand should really be, that the table remains locked until all rows have been retrieved, right? This is a very important thing to mention, you could tie up the whole database with a lock.
shaner at accretivetg dot com
22-May-2003 01:45
22-May-2003 01:45
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 );
break;
}
}
}
frappyjohn at dos2linux dot org
18-Feb-2003 07:21
18-Feb-2003 07:21
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 ...
david at php dot net
18-May-2002 06:25
18-May-2002 06:25
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.
chabotc at reviewboard dot com
21-Aug-2001 11:21
21-Aug-2001 11:21
Stefan,
unbuffered query sends a query to the server, and does not first download the results before sending them to the end-user (php in this case).
So what it means is that -normaly- you could do this:
$res1 = mysql_query("select some",$db_conn);
while ($row = mysql_fetch_row($res)) {
$res2 = mysql_query("select some other",$db_conn);
// do some other stuff
}
With an unbuffered query you could NOT do this, the result set from $res1 would be LOST on the second query.
However, it does not mean you -have- to fetch all rows ... just that the API does not save the result set in memory for you.
However, when using different db connections, it all works ofcource ...
For more information, please refer to the mysql manual, they have a lot of docs on query & unbuffered queries (the php api is just a basic wrapper around there native api's).