<?php if (查询条件) { ?>
    // 满足条件的语句
<?php } else { ?>
    // 不满足条件的语句
<?php } ?>

和大佬学到的代码代查询数据库的，贴子数和下载数查询相关:

<div class="text-muted small">
    <?php $downloads = db_find_one('attach',array('tid'=>$_thread['tid'],'filetype'=>'zip'));?>
    <?php if($downloads) {?>
    <span class="ml-2"><i class="icon-download"></i> <?php echo $downloads['downloads'];?></span>
    <?php }else{ ?>
    <!--{hook thread_list_inc_view_before.htm}-->
    <span class="ml-2 d-none"><i class="icon-eye"></i> <?php echo $_thread['views'];?></span>
    <!--{hook thread_list_inc_view_after.htm}-->
    <!--{hook thread_list_inc_posts_before.htm}-->
    <span class="ml-2"><i class="icon-comment-o"></i> <?php echo $_thread['posts'];?></span>
    <!--{hook thread_list_inc_posts_after.htm}-->
    <?php }?>
</div>