SQLDOU vs 一問から身につく SQL

SQLDOU is an educational app that visualizes SQL query execution plans with step by step animation. The third entry in the DOU series, following PAKEDOU (networking) and KURAUDOU (cloud). This time the theme is SQL. Enter a query and watch the execution plan generate automatically, then follow each row as it flows through filtering, sorting, joining and finally arrives at the result. WHAT YOU WILL LEARN • Full Scan vs Index Why scanning every row (full scan) is slow. See how much faster a B Tree index makes searches. Run the same SQL with both scan methods and compare speed in real time. • B Tree Index O(log n) Supports range queries such as greater than, less than, greater than or equal, less than or equal and equality. Watch the tree structure locate target rows efficiently through animation. • Hash Index O(1) Pro A high speed index specialized for equality searches. Experience the real execution time difference between Hash and B Tree. • WHERE and DISTINCT See each row pass or get skipped by the WHERE condition in real time with PASS or SKIP badges. Observe DISTINCT removing duplicates step by step. • JOIN Pro Visualize how rows from two tables are combined. See the batch process that waits for both sides before executing the join. • GROUP BY and ORDER BY Pro Watch aggregation such as COUNT, SUM, AVG, MAX and MIN and sorting such as ASC and DESC animate their internal processing. Observe how they buffer all rows before producing output. • Custom Quiz Mode v3.0 Pro Define your own table name, columns and rows, write any SQL you want, and save the quiz. Replay or edit later. Go beyond textbook examples and reproduce real world scenarios you care about. 20 MISSIONS Progress through 20 missions across 6 levels. • Level 1 SELECT and WHERE 5 missions SQL fundamentals • Level 2 Scan Methods 4 missions Full scan vs index speed comparison • Level 3 ORDER BY and DISTINCT 3 missions Pro • Level 4 GROUP BY 3 missions Pro • Level 5 JOIN 2 missions Pro • Level 6 Final Challenge 3 missions Index optimization Pro Each mission includes a prediction quiz. The Predict Execute Verify cycle encourages active learning. Star ratings up to three track your progress. EDUCATIONAL FEEDBACK • Auto comparison run the same SQL with full scan and index and see the speed difference automatically • Scan narration watch each row being checked in real time with PASS or SKIP verdict • Diagnostic comments context aware explanations Pro Why slow How to improve Background knowledge • Table data preview see actual data while making predictions FREE AND PRO Free • Level 1 and Level 2 missions total 9 missions • Basic diagnostics one line comment • B Tree index • Free mode Pro one time purchase • All 20 missions unlocked • Detailed diagnostics Why How to improve Background • Hash index support • Advanced SQL JOIN GROUP BY ORDER BY DISTINCT • Custom Quiz Mode build save and run your own quizzes • No ads WHO IS THIS FOR • Students and junior engineers learning SQL basics • Anyone who wants to intuitively understand why indexes are fast • Database beginners learning execution plans • Instructors looking for training supplements • Developers building a foundation in SQL performance tuning

【一問から身につく SQL とは】 SQLを「一問ずつ」確実に身につけるための学習アプリです。ストーリーとテーブル・データを見ながら、選択式の問題に取り組めます。解説では「なぜそうなるか」「よくある誤解」「実務ワンポイント」まで丁寧に解説し、暗記だけで終わらない理解を目指します。 【主な機能】 ・選択式の問題形式（ストーリー／テーブル・データ／SQL の見やすい構成） ・正解・不正解の履歴に基づく進捗表示 ・「誤答のみ表示」で苦手だけを集中的に復習 ・解説でつまずきやすい点を補強 【収録問題について】 リリース時点では全11問を収録しています。今後も問題を追加し、アプリアップデートで順次お届けする予定です（追加のタイミングや本数は開発状況により変わります）。 【料金】 ・一部の問題は無料で学習できます ・無料範囲を超える問題は、アプリ内課金（買い切り）でまとめて解放できます ・購入の復元に対応しています 【データ・プライバシー】 学習の進捗や解答履歴は、お使いの端末内に保存されます（当アプリ専用のアカウント登録は不要です）。 【利用規約】 本アプリの利用規約は、次のページでご確認いただけます。 https://root75125.github.io/sqlProblemPrivacy/terms-of-service.html ※本アプリの学習内容は一般的なSQLの理解を助けるものであり、特定の試験や資格の合格を保証するものではありません。