Chapter 13 · Data Analyst
Appendix B · Quick-reference glossary
~4 min read
| Term | Meaning |
|---|---|
| Aggregate function | COUNT, SUM, AVG, MIN, MAX; collapses many rows into one value. |
| CTE | Common Table Expression; a named query step using WITH for readable, staged SQL. |
| Dimension table | Descriptive context (who, what, when, where) joined to a fact table. |
| ELT | Extract, Load, Transform; modern pattern that transforms data inside the warehouse. |
| Fact table | Central table of measurements and events with foreign keys to dimensions. |
| Fan-out | Row multiplication from a one-to-many join that inflates a subsequent SUM. |
| Grain | What a single row in a table represents; define it before querying. |
| OLTP / OLAP | Operational write-optimized systems versus analytics read-optimized warehouses. |
| PII | Personally identifiable information; data that can identify a specific person. |
| p-value | Probability of seeing a result this extreme if the effect were truly zero. |
| Semantic layer | Central definitions of metrics so every dashboard agrees. |
| Slowly changing dimension | Pattern (Type 1/Type 2) for how a changing attribute is stored over time. |
| Star schema | Warehouse layout: one fact table surrounded by dimension tables. |
| Window function | Aggregation across a set of rows without collapsing them (RANK, LAG, SUM OVER). |
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