GROUP BY

Grouping rows, aggregating per group, HAVING, and WHERE versus HAVING.

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Notes

GROUP BY Fundamentals

GROUP BY collapses rows into one row per distinct key. Learn the single rule that governs the select list and how NULLs are grouped.

SQL

HAVING, and WHERE vs HAVING

HAVING filters groups after aggregation, WHERE filters rows before it. Learn when each applies, why using both is usually correct, and which is faster...

SQL

Multi Column Grouping and Grouping Rules

Grouping by several columns, grouping by expressions, and the totals features - ROLLUP, CUBE and GROUPING SETS - that add subtotal rows.