How to set up conditionals in page templates?

Question

I have created custom template page like this with a custom query on page showing only details fetch from my custom table not any post.

/*

Template Name:product

*/
<?php get_header(); ?>
<?php

    $data = $wpdb->get_results("myquery Here");
    foreach($data as $row)
    {
        product Name:  $row->p_name;
        prod price: $row->p_price;
?>
    <a href="">VIEW PRODUCT</a>

<?php
    }
?>
<?php get_footer();?>

I need help about when we click on "VIEW PRODUCT" then how can I redirect to next view_detail page?

For that can I create another *view_detail.php* page? What should I write on href="" with passing product_id, which I get on view_detail.php.

Answer 1

<?php
/*
Template Name:product
*/

get_header();

// check if product_id is not set or is empty string
if( !isset($_GET['product_id']) || '' == $_GET['product_id'] ) {
    // if so, run your query and display data
    $data = $wpdb->get_results("myquery Here");
    foreach($data as $row) {
        echo '<div>';
        echo '<p>Name:' . $row->p_name . '</p>';
        echo '<p>Price:' . $row->p_price. '</p>';
        // pass ID using GET
        echo '<p><a href="?product_id=' . $row->p_id . '">VIEW PRODUCT</a></p>';
        echo '</div>';
    }
}
else {
    // product_id is set and is not empty
    require('/path/to/view_detail.php');
}

get_footer();