sql-querying

原文涵盖的主题

• SQL Querying
• Quick Start
• When to Use
• Best Practices
• Readability
• Correctness
• Aggregation
• Performance

Writing correct, efficient SQL for analysis and applications. Reporting and ad-hoc analysis Application data access (ORMs under the hood) Data pipelines and ETL validation Any time you need relational answers Format queries with clear clauses and aliases Use CTEs (WITH) to break complex logic into steps Name columns meaningfully with aliases Add comments for non-obvious business logic Know join semantics: INNER vs LEFT vs FULL Watch for fan-out: one-to-many joins multiply rows Use DISTINCT deliberately, not by reflex Handle NULLs in WHERE/aggregations explicitly Aggregate with GROUP BY on non-aggregated columns Use window functions for rankings, running totals, deltas Filter with HAVING on aggregates, WHERE on rows Use COUNT(DISTINCT ...) for unique counts Only select needed columns Filter early with WHERE before joins Ensure indexes support filters and joins Avoid functions on indexed columns in WHERE 1. State the question you need answered in plain language. 2. Identify the tables and the join keys. 3. Write WHERE filters first, then joins, then aggregation. 4. Add GROUP BY / window functions for the desired shape. 5. Format with CTEs if the query is complex. 6. Check correctness

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