$wpdb->get_var not returning a result

I launched mysql and confirmed this query returns a result:

mysql> SELECT * FROM wp_posts WHERE post_parent = 68 AND post_type="attachment" AND post_name="side-logo-auto2" LIMIT 1;
1 row in set (0.00 sec)

In my template, I attempt same thing:

<?php if ( have_posts() ) : while ( have_posts() ) : the_post();

    //$wpdb->posts is wp_posts table
    //$post->ID is current post of post_type page, 
    //that is associated with page of this template

    global $wpdb;
    $image = $wpdb->get_var(
        $wpdb->prepare(
            "SELECT * FROM $wpdb->posts
             WHERE post_parent = %d
             AND post_type = %s
             AND post_name = %s
             LIMIT 1
            ",
            $post->ID,
            'attachment',
            'side-logo-auto2'
        )
    );
    echo "The image id is {$image->ID}";
    echo wp_get_attachment_image($image->ID);

endwhile; endif; ?> 

$post->ID returns 68. Yet, the value assigned to $image is not the record, but rather null.

$wpdb->get_var returns a single variable, but your SQL statement has SELECT * which returns a row of multiple columns.

You need to change your SQL statement to SELECT ID ... instead of SELECT * ...