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Sequence 079 — T2 - GROUP BY and aggregates
Stage: Technology Gate A — Relational Foundation
Source: CDMP Master Execution Manual
When / purpose
Summarize data without accidental double counting.
What you should learn
COUNT/SUM/AVG/MIN/MAX.GROUP BY.- Aggregation grain.
COUNT(*)vsCOUNT(column)awareness.
What to read / study
| Priority | Resource | Use now | Stop point |
|---|---|---|---|
| MUST | Technology Competency Roadmap | Use the exact active technology block and stopping boundary. | Do not study later blocks. |
| REFERENCE | Detailed Technology Competency Reference | Use only the section named by this card. | Do not convert the reference into a separate curriculum. |
Do this in order
- Create counts by status/location/category.
- Write the expected grain first.
- Compare pre-join and post-join row counts.
- Explain one double-counting risk.
Meridian application
Use Meridian synthetic data and the local lab environment only when the card calls for practice.
Create / save
Aggregation query set.
Stop / boundary
Stop at governance/data-management working depth; do not expand into DBA or engineering specialization.
Completion gate
You can aggregate correctly and explain why the numbers are not duplicated.
NEXT → Sequence 080 — T2 - HAVING, CASE and grouped diagnostics
Operationalized from the verified canonical 00C Master Execution Manual; not a verbatim transcription.
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