在限制之前如何计算匹配的行数？

Question

这是我的原始查询：

.py

它也有效并返回预期结果。现在我想在限制之前计算总行数。这是我的新查询似乎有效。我的意思是我不确定它是否正常工作，但是测试说它运作正常：

SELECT u.id user_id,
       u.avatar,
       u.date_time,
       CONCAT(u.user_fname, ' ', u.user_lname) name,
       sum($this->table_alias.vote_value) vote_value,
       sum($this->table_alias.score) score,
       $category_in_the_select AS tc $tag_in_the_select AS tt
FROM users u
JOIN reputations $this->table_alias ON u.id = $this->table_alias.owner_id $query_join
WHERE $time_limitation $query_where
GROUP BY user_id, u.avatar, u.date_time, name, tc, tt
ORDER BY score DESC, vote_value DESC
LIMIT :j, $this->per_page

正如您所看到的，我在应用SELECT x.*, @cnt cnt FROM (SELECT (@cnt := @cnt + 1) total, u.id user_id, u.avatar, u.date_time, CONCAT(u.user_fname, ' ', u.user_lname) name, sum($this->table_alias.vote_value) vote_value, sum($this->table_alias.score) score, $category_in_the_select AS tc $tag_in_the_select AS tt FROM users u CROSS JOIN (SELECT @cnt := 0) params JOIN reputations $this->table_alias ON u.id = $this->table_alias.owner_id $query_join WHERE $time_limitation $query_where GROUP BY user_id, u.avatar, u.date_time, name, tc, tt ORDER BY total) x ORDER BY x.score DESC, x.vote_value DESC LIMIT :j, $this->per_page 子句之前使用变量来计算结果。

注意到，我的方法比LIMIT函数快两倍。无论如何，我想知道的是，我的方法是正确的吗？或者没有任何保证，我不能依赖它？

再次，我测试了它，显然工作正常。