SQLDOU

SQL Query Execution Visualizer

Free · In‑App Purchases · Designed for iPad. Not verified for macOS.

See how databases really work. Watch full scans, B-Tree indexes, JOINs and more come alive with animation. v3.0 adds Custom Quiz Mode: build your own tables and 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

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Custom Quiz Mode now supports multiple tables and JOIN. The app is now available in 9 languages. - Custom Quiz Mode: define multiple tables and build JOIN queries with the visual builder - 9-language support: English, Japanese, Simplified Chinese, Traditional Chinese, Spanish, Portuguese (Brazil), Korean, German, French - UI polish and bug fixes throughout the app

Version 4.0

The developer, Fuji Bit Inc., indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .

  • Data Used to Track You

    The following data may be used to track you across apps and websites owned by other companies:

    • Identifiers

  • Data Not Linked to You

    The following data may be collected but it is not linked to your identity:

    • Identifiers

Privacy practices may vary, for example, based on the features you use or your age. Learn More

Accessibility

The developer has not yet indicated which accessibility features this app supports. Learn More

Information

Seller
  • Fuji Bit Inc.
Size
  • 10.2 MB
Category
  • Education
Compatibility
Requires iOS 16.0 or later.
  • iPhone
    Requires iOS 16.0 or later.
  • iPad
    Requires iPadOS 16.0 or later.
  • Mac
    Requires macOS 13.0 or later and a Mac with Apple M1 chip or later.
  • Apple Vision
    Requires visionOS 1.0 or later.
Languages
English and 8 more
  • English, French, German, Japanese, Korean, Portuguese, Simplified Chinese, Spanish, Traditional Chinese
Age Rating
4+
In-App Purchases
Yes
Copyright
  • © 2026 Fuji Bit
  • Developer Website
  • Privacy Policy

    • More by Fuji Bit Inc.

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