mysql_data_seek

(PHP 4, PHP 5, PECL mysql:1.0)

mysql_data_seek — Move internal result pointer

Description

bool mysql_data_seek ( resource $result , int $row_number )

mysql_data_seek() moves the internal row pointer of the MySQL result associated with the specified result identifier to point to the specified row number. The next call to a MySQL fetch function, such as mysql_fetch_assoc(), would return that row.

row_number starts at 0. The row_number should be a value in the range from 0 to mysql_num_rows() - 1. However if the result set is empty (mysql_num_rows() == 0), a seek to 0 will fail with a E_WARNING and mysql_data_seek() will return FALSE.

Parameters

result: The result resource that is being evaluated. This result comes from a call to mysql_query().
row_number: The desired row number of the new result pointer.

Return Values

Returns TRUE on success or FALSE on failure.

Examples

Example #1 mysql_data_seek() example


<?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);
?>

Notes

Note: The function mysql_data_seek() can be used in conjunction only with mysql_query(), not with mysql_unbuffered_query().


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 01:52


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 05:40


/*

    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
20-Apr-2005 08:53


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 april�s row.

b.steinbrink at g m x dot de
08-Dec-2004 11:09


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 12:12


/*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

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Last updated: Fri, 25 Jul 2008