MySQL 函数
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mysql_unbuffered_query

(PHP 4 >= 4.0.6, PHP 5)

mysql_unbuffered_query — 向 MySQL 发送一条 SQL 查询，并不获取和缓存结果的行

说明

resource mysql_unbuffered_query ( string $query [, resource $link_identifier ] )

mysql_unbuffered_query() 向 MySQL 发送一条 SQL 查询 query，但不像 mysql_query() 那样自动获取并缓存结果集。一方面，这在处理很大的结果集时会节省可观的内存。另一方面，可以在获取第一行后立即对结果集进行操作，而不用等到整个 SQL 语句都执行完毕。当使用多个数据库连接时，必须指定可选参数 link_identifier。

Note:

mysql_unbuffered_query() 的好处是有代价的：在 mysql_unbuffered_query() 返回的结果集之上不能使用 mysql_num_rows() 和 mysql_data_seek()。此外在向 MySQL 发送一条新的 SQL 查询之前，必须提取掉所有未缓存的 SQL 查询所产生的结果行。

参见 mysql_query()。

MySQL 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 向 MySQL 发送一条 SQL 查询，并不获取和缓存结果的行

用户评论:

crazyone at crazycoders dot net (27-May-2008 05:47)

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.

silvanojr at gmail dot com (12-May-2006 10:02)

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 02:18)

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 10:19)

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 (30-Nov-2003 01:57)

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 06:35)

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 12:45)

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 (18-Feb-2003 06:21)

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 05:25)

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.