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9 pages in this section.
The mental model behind a SQL query: why it is declarative, what order it actually executes in, and how that explains WHERE vs HAVING, NULL comparisons, and subquery-vs-join choices.
Learn fundamental SQL querying techniques in PostgreSQL with 10 examples covering SELECT, WHERE, ORDER BY, and LIMIT clauses.
Learn to use SQL GROUP BY, HAVING, and FILTER clauses to aggregate data, filter groups, and count subsets in PostgreSQL queries.
Learn how to use SQL subqueries with EXISTS to check for data presence, optimize queries with semi-joins, and avoid common pitfalls with IN and NULL.
Learn how UNION, INTERSECT, and EXCEPT combine SQL query results. Understand deduping behavior and practical PostgreSQL patterns.
Understand SQL NULL semantics, three-valued logic, and safe equality comparisons. Learn to use IS NULL, IS NOT NULL, and IS DISTINCT FROM.
Learn SQL querying best practices for performance and maintainability. Optimize projections, joins, and database operations to reduce latency.
A single-page roundup of every highlight bullet from the 8 pages in the SQL Querying section, grouped by source page so you can scan all 46 takeaways without opening each article individually.