okamuuu https://blog.hatena.ne.jp/okamuuu/ あいつの日誌β https://okamuuu.hatenablog.com/ SQL あらすじ 課題: それぞれの商品の前日の販売数と前々日の販売数の差を知りたい。 > select * from purchase_logs; +----+------------+-------------+------------+ | id | product_id | sales_count | created_on | +----+------------+-------------+------------+ | 1 | 1 | 100 | 2014-12-01 | | 2 | 2 | 100 | 2014-12-01 | | 3 | 3 | 100 | 2014-12-01 | |… 190 <iframe src="https://hatenablog-parts.com/embed?url=https%3A%2F%2Fokamuuu.hatenablog.com%2Fentry%2F2014%2F12%2F13%2F141003" title="それぞれの商品の販売数の前日比を SQL で求める - あいつの日誌β" class="embed-card embed-blogcard" scrolling="no" frameborder="0" style="display: block; width: 100%; height: 190px; max-width: 500px; margin: 10px 0px;"></iframe> Hatena Blog https://hatena.blog 2014-12-13 14:10:03 rich https://okamuuu.hatenablog.com/entry/2014/12/13/141003 1.0 100%