SQL, from the ground up.
Build a working foundation in joins, window functions, and transactions. Small datasets make each idea easy to inspect.
01
Reference · 3 min
02SQL joins: a small reference with predictable results
Use a tiny customer-and-order dataset to see inner joins, left joins, and the filter placement that changes their meaning.
Tutorial · 3 min
03Window functions: keep the rows, add the context
Calculate a running total and rank orders within each customer without collapsing the underlying rows.
Engineering guide · 3 min
A transaction is a boundary, not a magic shield
Separate atomicity from isolation and learn why two individually correct transactions can still surprise each other.