按照,产品的,总点击量,由高到低,进行排序

$list = $this->table->field("id, add_date, count(ip) ip_count, product_id, count(product_id) product_id_count, category_id")
    ->where($condition)
    ->group(product_id)
    ->order(product_id_count desc)
    ->order(ip_count desc)
    ->limit($page->firstRow.,.$page->listRows)
    ->select();

根据一列,只去重,不统计总点击量:

count(DISTINCT product_id) product_id_count,
->group(product_id) 

根据一列,统计总点击量,同时,去重:

count(product_id) product_id_count
->group(product_id)

根据,多列,count,group,order:

$list = $this->table->field("id, add_date, count(ip) ip_count, product_id, count(product_id) product_id_count, category_id")
    ->where($condition)
    ->group(product_id)
    ->order(product_id_count desc)
    ->order(ip_count desc)
    ->limit($page->firstRow.,.$page->listRows)
    ->select();
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