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 ...
mysql_unbuffered_query
(PHP 4 >= 4.0.6, PHP 5)
mysql_unbuffered_query — Envia uma query para o MySQL, sem retornar e colocar em buffer as linhas do resultado
Descrição
mysql_unbuffered_query
( string
$query
, resource $link_identifier = ?
) : resource
mysql_unbuffered_query() envia uma
query SQL para MySQL, sem retornar e colocar em buffer as linhas do resultado automaticamente,
como mysql_query() faz. por um lado, isto salva uma quantidade considerável de memória
em query que produzem um resultado grandes. por outro lado, você pode começãr a trbalhar com o resultado imediatamente após
a primeira linha ser retornada: você não tem que esperar que toda a query SQL seja realizada. Quando usar multiplas conexões com
o banco de dados, você deve especificar o parametro opcional
link_identifier.
Nota:
Os beneficios de mysql_unbuffered_query() vem com um custo: você não pode usar mysql_num_rows() e mysql_data_seek() no resultado retornado por mysql_unbuffered_query(). Você também tem que pegar todas as linhas de uma query SQL sem buffer antes de poder enviar uma nova query SQL para o MySQL.
Veja também mysql_query().
add a note
User Contributed Notes 5 notes
frappyjohn at dos2linux dot org ¶
21 years ago
crazyone at crazycoders dot net ¶
15 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 ¶
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.
shaner at accretivetg dot com ¶
20 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;
}
}
}
?>
david at php dot net ¶
21 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.
