(PHP 4 >= 4.0.6, PHP 5)
mysql_unbuffered_query — Send an SQL query to MySQL without fetching and buffering the result rows.
This extension was deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API guide and related FAQ for more information. Alternatives to this function include:
$query
[, resource $link_identifier = NULL
] )
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.
queryThe SQL query to execute.
Data inside the query should be properly escaped.
link_identifierThe MySQL connection. If the
link identifier is not specified, the last link opened by
mysql_connect() is assumed. If no such link is found, it
will try to create one as if mysql_connect() was called
with no arguments. If no connection is found or established, an
E_WARNING level error is generated.
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:
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.
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.
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 ...
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.
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.
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;
}
}
}
?>
