Observed arrival · 2026-11-11
Wrong Join turns SQL practice into a debugging test
An interactive SQL tutor asks learners to diagnose query errors, run their own queries, and earn levels by demonstrating what they know.
○Open
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$Paid
†Ads
✦Pretty
●Pro
◎Niche
◉Human
⚑Risk
ƒJS
- For
- SQL learners practicing joins, aggregation, and window functions
- Worth noticing
- The sample LEFT JOIN exercise is meant to include 40 customers, but its WHERE clause leaves 30 rows.
Field notes
The described session starts with about five placement questions, then moves through a map of eight skills. A wrong answer leads to a narrower follow-up, while earlier skills can return in unannounced review and a failed review can lower a level. The site's level system distinguishes assisted work from unaided recall; its highest level also asks learners to handle an edge case and explain it.
Observed signals
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Editorial observations of this landing page, not a rating.
○OpenPublic substance visible
$PaidCommerce or pricing visible
✦PrettyNotable craft visible
●ProPolished or operationally mature
◎NicheUnusually specific use
One card from the complete issue