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SQL

Querying, joins, indexes, transactions, and query optimization

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  1. 00 SQL — Roadmap Your path from writing your first SELECT to designing schemas and shipping zero-downtime migrations.
  2. 01 The Relational Model & Basic Queries Tables, rows, columns, types — and the SELECT statement that pulls data back out.
  3. 02 Filtering, Grouping & Aggregation Collapse many rows into summary answers with COUNT, SUM, GROUP BY, and HAVING.
  4. 03 Joins Combining rows from multiple tables — the operation that makes relational databases relational.
  5. 04 Subqueries & CTEs Queries inside queries — scalar, correlated, derived tables, WITH clauses, and recursion.
  6. 05 Indexes & Query Plans How the database finds rows fast — B-tree indexes, EXPLAIN, and when an index is useless.
  7. 06 Transactions & Isolation Levels ACID, the four isolation levels, MVCC, and the locks and deadlocks that keep concurrent writes correct.
  8. 07 Window Functions Aggregate-like calculations that keep every row — rankings, running totals, and row-to-row comparisons.
  9. 08 Query Optimization & Performance Reading plans in anger, killing N+1 queries, paginating at scale, and avoiding the classic anti-patterns.
  10. 09 Schema Design & Migrations Constraints, normalization, generated columns, and the expand/contract pattern for zero-downtime change.