SQLDOU vs D426 Mastery

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

Stop stressing about D426. Start mastering it. D426 Mastery is the #1 study app built specifically for WGU students preparing for the D426 Data Management Foundations Objective Assessment. Every flashcard, every quiz question, and every sample database is designed to help you pass your OA with confidence. SPACED REPETITION FLASHCARDS - 400+ flashcards covering every D426 competency - Anki-style SM-2 algorithm that adapts to your knowledge - Cards you struggle with show up more often -- cards you know fade away - Search, browse, and filter by topic MOCK OA EXAMS - 200+ exam-style multiple choice questions - Randomized answer positions so you actually learn, not memorize patterns - Review every missed question with the correct answer and detailed explanation - Topic-based quizzes to target your weak areas REAL SQL PLAYGROUND - Write and execute actual SQL queries -- not just theory - 5 realistic sample databases: University, Sales, Hospital, Employee, Inventory - Syntax highlighting, formatted result tables, and query history - Practice DDL and DML commands against real data INTERACTIVE ER DIAGRAM BUILDER - Drag-and-drop entities, attributes, and relationships - Crow's Foot notation with cardinality validation - Build and visualize database designs hands-on COMPLETE TOPIC COVERAGE - Relational Model Concepts - ER Diagrams and Crow's Foot Notation - Primary Keys and Foreign Keys - Database Normalization (1NF, 2NF, 3NF, BCNF) - SQL DDL Commands (CREATE, ALTER, DROP) - SQL DML Commands (SELECT, INSERT, UPDATE, DELETE) - Conceptual, Logical and Physical Data Models - DBMS Architecture and ACID Properties SMART PROGRESS TRACKING - Mastery percentage for every topic - Radar chart showing your strengths and weak spots - OA Readiness score -- know exactly when you're ready to test - Study streak counter and daily session timer - Detailed statistics: cards reviewed, quizzes taken, accuracy rate SEARCHABLE GLOSSARY - 90+ database terms with clear definitions - Organized by category for quick reference - Perfect for last-minute review before your OA FREE VS PREMIUM Free includes: - 50 flashcards with full spaced repetition - 1 mock OA exam per day - 1 sample SQL database - Complete glossary - Basic study statistics Premium unlocks: - All 400+ flashcards - Unlimited mock OA exams - All 5 SQL databases - Missed questions review after every quiz - OA Readiness score - Interactive ER Diagram Builder - Advanced analytics Premium is available as a monthly subscription ($7.99/month, auto-renewing) or a one-time lifetime purchase ($24.99). Monthly subscriptions automatically renew unless canceled at least 24 hours before the end of the current billing period. Manage or cancel anytime in your Apple ID account settings. WORKS 100% OFFLINE No internet required. No account needed. No data leaves your device. Study anywhere -- on the bus, in bed, between classes. BUILT BY WGU STUDENTS, FOR WGU STUDENTS We know the D426 OA because we've been there. Every flashcard and quiz question is mapped to actual course competencies so you study what matters. D426 Mastery is an independent study aid and is not affiliated with, endorsed by, or sponsored by Western Governors University. Support: https://johndisalle.github.io/D426/support Terms of Service: https://johndisalle.github.io/D426/terms-of-service Privacy Policy: https://johndisalle.github.io/D426/privacy-policy