Count records from a mysql table - php

Question

I have this carousel that I want to make dynamic. To operate, the carousel must begin with a class
<div class="item active">
and must stay out of the while loop. After the fourth record extract, the class must become simply
<div class="item">
In summary:
0 to 4 -> <div class="item active">
5 to 8 --><div class="item">
9 to 12 --> <div class="item"> ....so on
How do I count the records extracted?
Thanks
<?php
$banner = "SELECT * FROM tbl_banner";
$result_b = dbQuery($banner);
// here --> <div class="item active"> or <div class="item">
while($row_b = dbFetchAssoc($result_b)) {
extract($row_b);
?>
<div class="col-md-3">
<div class="w-box inverse">
<div class="figure">
<img alt="" src="banner/<?php echo $img; ?>" class="img-responsive">
<div class="figcaption bg-2"></div>
<div class="figcaption-btn">
<i class="fa fa-plus-circle"></i> Zoom
<i class="fa fa-link"></i> View
</div>
</div>
<div class="row">
<div class="col-xs-9">
<h2><?php echo $img_title; ?></h2>
<small><?php echo $img_desc; ?></small>
</div>
</div>
</div>
</div>
<?php
}
?>

Answer 1

You can use num_rows to see how many rows were returned. Unfortunately from your question I can't tell whether you're using MySQL, MySQLi or PDO as it seems you pass all your queries into a class.
For MySQLi use the following:
$num = $result_b->num_rows;

Answer 2

SELECT COUNT(*) AS cnt FROM tbl_banner
OR
count( $res ); # in php
Also see: Which is fastest? SELECT SQL_CALC_FOUND_ROWS FROM `table`, or SELECT COUNT(*)

Answer 3

I don't understand....
I would like a result like this, explained in this way:
$query ="SELECT .....
<div class="row">
<div class="item active">
while {
<div1>...</div>
<div2>...</div>
<div3>...</div>
<div4>...</div>
} //end while
</div>
</div>
<div class="row">
<div class="item">
while {
<div4>...</div>
<div6>...</div>
<div7>...</div>
<div8>...</div>
} //end while
etc etc