Window functions: keep the rows, add the context
Calculate a running total and rank orders within each customer without collapsing the underlying rows.
SQL fundamentals.
Build a practical foundation in queries, aggregation, joins, and transactions.
Put it into practice.
Guides & tutorialsAnalyze a Parquet file with DuckDB and SQL
Go from a local file to a useful analytical query without standing up a database server.
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.
SQL 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.