How can I count the numbers of rows that a MySQL query returned?

You can use the mysqli_num_rows() function to count the number of rows that a MySQL query returned in PHP.

Here's an example of how to use mysqli_num_rows():

<?php

$link = mysqli_connect("localhost", "my_user", "my_password", "my_db");

/* check connection */
if (mysqli_connect_errno()) {
  printf("Connect failed: %s\n", mysqli_connect_error());
  exit();
}

$query = "SELECT * FROM my_table WHERE column_name = 'some value'";
$result = mysqli_query($link, $query);

$num_rows = mysqli_num_rows($result);

printf("Result set has %d rows.\n", $num_rows);

/* close connection */
mysqli_close($link);

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This code connects to a MySQL database, executes a SELECT query, and then uses mysqli_num_rows() to count the number of rows returned by the query. It then prints out the number of rows.