SQL and PostgreSQL Guide: From First Query to Production

What a relational database is, running PostgreSQL, a small shop schema, SELECT, WHERE, NULL logic, and INSERT, UPDATE and DELETE with RETURNING.

Primary and foreign keys, inner, left, right, full and cross joins with drawn result tables, self joins and the NULL trap in left joins.

COUNT, SUM and AVG, GROUP BY rules, HAVING versus WHERE, FILTER, date_trunc reports and the order a SELECT is evaluated.

Scalar, IN and EXISTS subqueries, WITH queries, a recursive category tree, ranking, LAG and LEAD, running totals and top-N per group.

Identity versus UUID keys, normal forms with a flat-to-normalised redesign, ON DELETE, enums, money, timestamptz and soft deletes.

How a B-tree helps, composite, covering and partial indexes, and reading real EXPLAIN ANALYZE plans on a million rows.

Why an index turns 812 ms into 0.09 ms, and why it slows every write. How B-trees keep sorted pages updated in place, how LSM-trees append and compact for huge write rates, and how to design indexes from real queries.

Store each fact once and writes stay correct; copy facts on purpose and reads get fast. Normal forms in plain English, the anomalies they prevent, the denormalisation toolkit, and how to keep copies in sync.

Atomicity, read committed versus repeatable read versus serializable with two real sessions, row locks, SKIP LOCKED, deadlocks and retries.

JSONB with GIN indexes, full-text search, arrays, upserts, and expand-and-contract migrations that do not lock a busy table.

Two people book the last seat; a transfer crashes halfway. What ACID really promises, the write-ahead log behind durability, the five anomalies isolation levels do (and don't) prevent, and the practical fixes for real race conditions.

B-tree indexes, reading EXPLAIN ANALYZE, transactions and isolation levels, and the race conditions they stop, like selling too many items.

Prisma 7, migrations, relations, transactions, N+1, raw queries, and the SQL behind it.

Next.js metadata and sitemaps, locale routing and plurals, service workers, window functions, JSONB, EXPLAIN, locks, vacuum and PgBouncer.

“SQL or NoSQL?” is the wrong question; the right one is “what shape is my data, and how will I read and write it?” The relational model and the four NoSQL families — key-value, document, wide-column and graph — what each is good at, the myths to drop, and a sensible default.