sql

For developers who write SQL that must be both correct and fast, covering the specifics of SELECT, JOIN, aggregation and GROUP BY traps, subqueries, window functions (ROW_NUMBER/RANK/LAG), NULL semantics, transactions, and DDL — each with a locally runnable example showing the expected behavior.

A MySQL command handbook for DBAs, backends, and data analysts, covering database & table management, CRUD, index optimization and slow-query localization with EXPLAIN, user privileges, logical backup & recovery, and replication — highlighting operations that can lock tables or stall replication.

A PostgreSQL command handbook for backend engineers, DBAs, and data analysts, covering connection & role management, database & table operations, EXPLAIN analysis, lock & transaction troubleshooting, pg_dump/pg_restore backup & recovery, and streaming replication, with paths for locating lock waits and table bloat.

A SQL JOIN reference for writing multi-table queries correctly, covering INNER, LEFT/RIGHT/FULL OUTER, CROSS, self-joins, USING/natural joins, and when a correlated subquery with EXISTS beats a JOIN — plus the row-duplication pitfall of joins on one-to-many tables.

A Knex.js query-builder reference for Node.js developers who want type-safe, database-agnostic SQL, covering CRUD, joins, aggregation & grouping, transactions with rollback, schema building, raw queries, and debug() to inspect the generated SQL.

A reference for developers who need a zero-config embedded database in a single portable file, covering creation & connection, table operations, CRUD, indexes & constraints, transactions, CSV import/export, and the sqlite3 CLI — plus the WAL-mode and concurrent-write-lock gotchas.