MySQL 函数
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PHP手册

mysql_data_seek

(PHP 4, PHP 5)

mysql_data_seek — 移动内部结果的指针

说明

bool mysql_data_seek ( resource $result , int $row_number )

mysql_data_seek() 将指定的结果标识所关联的 MySQL 结果内部的行指针移动到指定的行号。接着调用 mysql_fetch_row() 将返回那一行。

row_number 从 0 开始。row_number 的取值范围应该从 0 到 mysql_num_rows - 1。但是如果结果集为空（mysql_num_rows() == 0），要将指针移动到 0 会失败并发出 E_WARNING 级的错误，mysql_data_seek() 将返回 FALSE。

参数

result

resource 型的结果集。此结果集来自对 mysql_query() 的调用。

row_number

想要设定的新的结果集指针的行数。

返回值

成功时返回 TRUE， 或者在失败时返回 FALSE.

范例

Example #1 mysql_data_seek() 例子

<?php
$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
    die('Could not connect: ' . mysql_error());
}
$db_selected = mysql_select_db('sample_db');
if (!$db_selected) {
    die('Could not select database: ' . mysql_error());
}
$query = 'SELECT last_name, first_name FROM friends';
$result = mysql_query($query);
if (!$result) {
    die('Query failed: ' . mysql_error());
}
/* fetch rows in reverse order */
for ($i = mysql_num_rows($result) - 1; $i >= 0; $i--) {
    if (!mysql_data_seek($result, $i)) {
        echo "Cannot seek to row $i: " . mysql_error() . "\n";
        continue;
    }

    if (!($row = mysql_fetch_assoc($result))) {
        continue;
    }

    echo $row['last_name'] . ' ' . $row['first_name'] . "<br />\n";
}

mysql_free_result($result);
?>

注释

Note: Suggested alternatives

Use of this extension is discouraged. Instead, the MySQLi or PDO_MySQL extension should be used. See also MySQL: choosing an API for more information.

Alternatives to this function include:

Note:

mysql_data_seek() 只能和 mysql_query() 结合起来使用，而不能用于 mysql_unbuffered_query()。

参见

MySQL 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 移动内部结果的指针

用户评论:

saeed at photobookworldwide dot com (26-Nov-2011 02:30)

Here, you can find the current pointer of selected row easily:

<?php
//selected row with id=4
$id    =    "4";

$result    =    mysql_query("select * from jos_components");

$num    =    mysql_num_rows($result);

for($i=0;$i<$num;$i++){
   
    mysql_data_seek($result,$i);
 
    $row    =    mysql_fetch_assoc($result);
   
    if($row['id']    ==    $id){
       
        $pointer    =    $i;
    }

 
}

// current pointer for selected row
echo $pointer;
?>

webmail7 at suddenlink dot net (29-Apr-2009 06:48)

The mysql_query() function using the SELECT, SHOW, DESCRIBE, EXPLAIN or other statements returning a resultset, by default uses a TABLES INDEX, or simply the RECORD INSERT ORDER, in creating the resultset.

When using the mysql_data_seek() function along with a mysql_query() function using the SELECT, SHOW, DESCRIBE, EXPLAIN or other statements returning a resultset, and your desire is to SELECT A SPECIFIC ROW based upon the CONTENTS of a SPECIFIC FIELD then be sure to use the ORDER statement in your query or the mysql_data_seek() function may have unpredictable results.

Example (Find Last Record):

==============================================

<?php

$query="SELECT * FROM `team` ORDER BY `team`.`id` ASC";
$result=mysql_query($query);
$last_row = mysql_num_rows($result) - 1;
if (mysql_data_seek($result, $last_row)) { //Set Pointer To LAST ROW in TEAM table.

     $row = mysql_fetch_row($result); //Get LAST RECORD in TEAM table
     $id = $row[0] + 1; //New Team ID Value
     // more code here ...

} else { //Data Seek Error

    echo "Cannot seek to row $last_row: " . mysql_error() . "\n";       

}

?>

==============================================

** Note:

1. The above example code relates to a MYSQL table named 'team' similar to this:

+-ID-+ TEAM NAME-+
| 49 |  Team 49  |
| 33 |  Team 33  |
| 84 |  Team 84  |
| 07 |  Team 07  |
+----+-----------+
** Records shown in the order inserted (i.e. TABLE NOT INDEXED)

2. In the above example code the field named ID is NOT set to AUTO-INCREMENT (i.e. field value set programmatically).

3. Wanting to insert a new team with a team number higher that the highest team number used, simply using the following code snippet

==============================================

<?php

$query="SELECT * FROM `team`";

?>

==============================================

resulted in an ERROR when using the mysql_data_seek() function  to select the record with the highest ID value.

4. Use of the ORDER statement in the query corrected the error/problem.

Hope this helps someone.

Daniel (28-Aug-2008 10:59)

Here is a simple function to "peek" at the position of the internal pointer in a query result:

<?php
function mysql_pointer_position($result_set) {
        $num_rows = mysql_num_rows($result_set);
        $i = 0;
        while($result = mysql_fetch_array($result_set)) {
            $i++;
        }
        $pointer_position = $num_rows - $i;

//Return pointer to original position
        if($pointer_position <= $num_rows - 1) {
            mysql_data_seek($result_set, $pointer_position);
        }
        return $pointer_position;
    }
?>

Guy Gordon (27-Jun-2007 09:26)

I needed to "peek" at the next record in order to see if fetching it would go too far.  So I want to do a fetch, followed by seek(-1).
 
I could find no function to move the internal row pointer relative to it's current position, or to retrieve it as a row number as required by mysql_data_seek().  This limits the function's usefulness to resetting the row to 0, unless you track the row number yourself.

If you use a While loop to step through the results, you can increment a tracking index at the bottom of the loop.  But be sure never to use Continue; which would bypass your index.  And document this restriction for the person who needs to maintain your code.  It's probably better to use a For loop, which makes the index explicit. 

In either case be sure to range check the index when you manipulate it.  E.G. When I "peek" at the next record I must check for index>=count (end of data).  Or if I decrement the index, make sure it does not go negative.  Again, document why you are coding it this way, so the next programmer doesn't "correct" the inelegant code.

(30-May-2006 09:52)

A helpful note about the 'resource' data type.

Since the 'resource' variable is pointing to a row in a result set at any given time, you can think of it as being passed to this function by reference every time you pass it or assign it to a variable.

<?

$sql = "SELECT * from <table>";
$result = mysql_query($sql);
$temp_result = $result;

while ($row = mysql_fetch_assoc($temp_result)) {
    // do stuff with $row
}

while ($row = mysql_fetch_assoc($result)) {
    // This code will never run because the 'resource' variable is pointing past the end of the result set,
    // even though it was *not* assigned by reference to $result2.
}

?>

Therefore, the following snipits are functionally identical:

<?

// Start snipit 1

$sql = "SELECT * from <table>";
$result = mysql_query($sql);

while ($row = mysql_fetch_assoc($result)) {
    // do stuff with $row
}

mysql_data_seek($result, 0);

while ($row = mysql_fetch_assoc($result)) {
    // do other stuff with $row
}

// Start snipit 2

$sql = "SELECT * from <table>";
$result = mysql_query($sql);
$temp_result = $result;

while ($row = mysql_fetch_assoc($temp_result)) {
    // do stuff with $row
}

mysql_data_seek($result, 0);

while ($row = mysql_fetch_assoc($temp_result)) {
    // do other stuff with $row
}

?>

jonybd at yahoo dot com (27-Jun-2005 01:40)

/*
    helpfull for real time databases query
    - Query one time
    - Retreive data twice from the same query
    - mysql_data_seek *

*/

include("p_MySql_Connection.php");

$v_Query    =     "SELECT f1 from t1";
           
$v_Result     =     mysql_query($v_Query, $v_RS);

/*
    First loop for one single query
*/
while ($row = mysql_fetch_array($v_Result,MYSQL_NUM)) {
    $v_total = $v_total + $row[1];
}
    echo $v_total;
           

/*
    Retreive data
*/
$v_Re     =     mysql_data_seek($v_Result,0);
if (!$v_Re){
    echo 'MySql data seek Error' .  mysql_error();
}

/*
    Second loop for one single query
*/           
while ($row = mysql_fetch_array($v_Result,MYSQL_NUM)) {
    echo $row[0];

}

arturo_b at hotmail dot com (21-Apr-2005 04:53)

hello, this script would be easy to understand for those that are novice in php whose want to understand about this function:

the table "user" have 2 columns "id" and "name".
"user" content:
position 0: "id"=195342481 "name"='Arthur'
position 1: "id"=179154675 "name"='John'
>>position 2<<: "id"=157761949 "name"='April' >>third row<<
position 3: "id"=124492684 "name"='Tammy'
position 4: "id"=191346457 "name"='Mike'

<?php
  mysql_connect("localhost", "root")
  mysql_select_db("test");
  $sql = mysql_query("select * from user");
  mysql_data_seek($sql, 2);
  echo "<table border=1>";
  while ($row = mysql_fetch_row($sql)){
    echo "<tr><td>$row[0]</td><td>$row[1]</td></tr>";
  }
  echo "</tabla>";
?>

explanation:
mysql_data_seek move internal result pointer to the third row of table user. Thus mysql_fetch_row will begin by aprils row.

b.steinbrink at g m x dot de (09-Dec-2004 07:09)

to kennethnash1134 at yahoo dot com

your loop can be done like this as well and i guess this is faster:

$r=mysql_query("select user,id,ip from accounts limit 10");

unset($users); // Just to be sure
while($users[] = mysql_fetch_row);
array_pop($users); // Drop the last entry which is FALSE

kennethnash1134 at yahoo dot com (26-Mar-2004 08:12)

/*here is a nice function for converting a mysql result row set into a 2d array, a time saver if need small data from several rows, saves you from having to do Alot of queries... would be nice to have this built into PHP future versions :) */

// simple example query
$r=mysql_query("select user,id,ip from accounts limit 10");

//starts the for loop, using mysql_num_rows() to count total
//amount of rows returned by $r
for($i=0; $i<mysql_num_rows($r); $i++){
             //advances the row in the mysql resource $r
    mysql_data_seek($r,$i);
             //assigns the array keys, $users[row][field]
    $users[$i]=mysql_fetch_row($r);
}

//simple, hope someone can use it :)
// -Kenneth Nash