mysql_thread_id
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)
mysql_unbuffered_query — Send an SQL query to MySQL, without fetching and buffering the result rows
Описание
resource mysql_unbuffered_query
( string $query
[, resource $link_identifier
] )
mysql_unbuffered_query() sends a SQL query query to MySQL, without fetching and buffering the result rows automatically, as mysql_query() does. 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 after the first row has been retrieved: you don't have to wait until the complete SQL query has been performed. When using multiple DB-connects, you have to specify the optional parameter link_identifier .
Параметри
- query
-
A SQL query
Data inside the query should be properly escaped.
- link_identifier
-
Връзката към MySQL. Ако не е указана, се използва последната създадена връзка от mysql_connect(). Ако не намери такава връзка, ще направи опит да установи връзка, все едно е изпълнена mysql_connect() без параметри. Ако случайно не е намерена или създадена никаква връзка, ще се генерира предупреждение от ниво E_WARNING.
Връщани стойности
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.
Бележки
Забележка: 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(). You also have to fetch all result rows from an unbuffered SQL query, before you can send a new SQL query to MySQL.
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User Contributed Notes
mysql_unbuffered_query
crazyone at crazycoders dot net
27-May-2008 09:47
silvanojr at gmail dot com
12-May-2006 02:02
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 06:18
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
01-Apr-2004 02:19
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.)
<?php
$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
29-Nov-2003 05:57
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 10:35
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
21-May-2003 04:45
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:
<?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;
}
}
}
?>
frappyjohn at dos2linux dot org
17-Feb-2003 10:21
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
17-May-2002 09:25
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.