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Sequence 078 — T2 - LEFT JOIN and missing relationships
Stage: Technology Gate A — Relational Foundation
Source: CDMP Master Execution Manual
When / purpose
Use outer joins for governance/data-quality investigation.
What you should learn
LEFT JOIN.- Unmatched rows.
- NULLs created by absence of a match.
- Difference from filtering after a join.
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
- Find source rows lacking expected related records.
- Explain whether absence is valid, unknown or a quality issue.
- Create one incorrect
WHEREcondition that destroys the outer-join effect, then repair it.
Meridian application
Use Meridian synthetic data and the local lab environment only when the card calls for practice.
Create / save
LEFT JOIN diagnostic query.
Stop / boundary
Stop at governance/data-management working depth; do not expand into DBA or engineering specialization.
Completion gate
You can use a LEFT JOIN to identify unmatched records and explain the result.
NEXT → Sequence 079 — T2 - GROUP BY and aggregates
Operationalized from the verified canonical 00C Master Execution Manual; not a verbatim transcription.
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