这句sql是什么意思，请大神指教
<code>SELECT `sid`,count(*) AS count FROM `hx_shop_period` GROUP BY sid ORDER BY count desc LIMIT 5</code>
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这句sql是什么意思，请大神指教
<code>SELECT `sid`,count(*) AS count FROM `hx_shop_period` GROUP BY sid ORDER BY count desc LIMIT 5</code>
查找 hx_shop_peried表，根据条件group by sid（以sid为分组）查找出sid字段和sid出现的次数，生成一个结果集。
然后对这个结果集进行降序排序，取出前5行
非大神...
1. SELECT 很好理解，指定要返回哪些值，这里是返回 sid 和 count
2. FROM 也很好理解，从 hx_shop_period 这张表里返回...
3. 那么 count(*) AS count 怎么理解？
count(column_name) 是用于计算数量的，括号内是列的名字，如果为*表示表中的记录数。
但这里与 GROUP BY 连用，意思是计算各个 sid 的数量。
4. ORDER BY / LIMIT 都很好理解就是按照什么排序，和限制返回数目
连起来就是从 hx_shop_period 这张表里返回5条 sid 和 sid 的数量的消息，结果按照数量降序。
聚合sid,sid一样的数量加一起放一个字段，由数量降序只取5条记录
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