Database management systems notes
Aggregation & Grouping
Turning many rows into one number, per group, without getting the count wrong. Every section is a drawn page beside a clear written explanation, about 19 minutes in all.
- Chapter 10 of 34
- About 19 minutes
- 8 sections
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In this chapter
- The five aggregate functions
- The three COUNTs
- GROUP BY: one result row per group
- HAVING: filtering groups
- Grouping by several columns
- DISTINCT and GROUP BY
- Aggregating across joined tables
- Checking an aggregate before you believe it
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