> One should not use mysqli_use_result() if a lot of processing on the client side is performed, since this will tie up the server and prevent other threads from updating any tables from which the data is being fetched.
Another way of understanding the "blocking" behavior of this "use_result" method is that by using this method (or the MYSQLI_USE_RESULT flag on the "query" method), if attempting to run a second query of any kind - updates, inserts, selects, or other - while still working with these first results, the second query will fail. Checking mysqli->error, you should get a "Commands out of sync" error on the second query call.
However, if you use the "store_result" method (or the default MYSQLI_STORE_RESULT flag on the "query" method) instead, the second query will execute just fine.
Just to demonstrate this "blocking" behavior of this "use_result" method, the second query on line 7 below would otherwise fail if you instead used "use_result" on line 3:
<?php
$mysqli->real_query('SELECT * FROM `test`');
$query = $mysqli->store_result();
while ($row = $query->fetch_assoc()) {
$id = (int) $row['id'];
$query2 = $mysqli->query("UPDATE `test` SET `label` = md5(rand()) WHERE `id` = $id");
}
?>
mysqli::use_result
mysqli_use_result
(PHP 5, PHP 7, PHP 8)
mysqli::use_result -- mysqli_use_result — Initiate a result set retrieval
Description
Object-oriented style
Procedural style
Used to initiate the retrieval of a result set from the last query executed using the mysqli_real_query() function on the database connection.
Either this or the mysqli_store_result() function must be called before the results of a query can be retrieved, and one or the other must be called to prevent the next query on that database connection from failing.
Note:
The mysqli_use_result() function does not transfer the entire result set from the database and hence cannot be used functions such as mysqli_data_seek() to move to a particular row within the set. To use this functionality, the result set must be stored using mysqli_store_result(). One should not use mysqli_use_result() if a lot of processing on the client side is performed, since this will tie up the server and prevent other threads from updating any tables from which the data is being fetched.
Parameters
This function has no parameters.
Return Values
Returns an unbuffered result object or false if an error occurred.
Errors/Exceptions
If mysqli error reporting is enabled (MYSQLI_REPORT_ERROR) and the requested operation fails,
a warning is generated. If, in addition, the mode is set to MYSQLI_REPORT_STRICT,
a mysqli_sql_exception is thrown instead.
Examples
Example #1 mysqli::use_result() example
Object-oriented style
<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$query = "SELECT CURRENT_USER();";
$query .= "SELECT Name FROM City ORDER BY ID LIMIT 20, 5";
/* execute multi query */
if ($mysqli->multi_query($query)) {
do {
/* store first result set */
if ($result = $mysqli->use_result()) {
while ($row = $result->fetch_row()) {
printf("%s\n", $row[0]);
}
$result->close();
}
/* print divider */
if ($mysqli->more_results()) {
printf("-----------------\n");
}
} while ($mysqli->next_result());
}
/* close connection */
$mysqli->close();
?>Procedural style
<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "world");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
$query = "SELECT CURRENT_USER();";
$query .= "SELECT Name FROM City ORDER BY ID LIMIT 20, 5";
/* execute multi query */
if (mysqli_multi_query($link, $query)) {
do {
/* store first result set */
if ($result = mysqli_use_result($link)) {
while ($row = mysqli_fetch_row($result)) {
printf("%s\n", $row[0]);
}
mysqli_free_result($result);
}
/* print divider */
if (mysqli_more_results($link)) {
printf("-----------------\n");
}
} while (mysqli_next_result($link));
}
/* close connection */
mysqli_close($link);
?>The above examples will output:
my_user@localhost ----------------- Amersfoort Maastricht Dordrecht Leiden Haarlemmermeer
See Also
- mysqli_real_query() - Execute an SQL query
- mysqli_store_result() - Transfers a result set from the last query
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Anonymous ¶
12 years ago
