Read an error before changing code
Tool Setup & Troubleshooting · Work on your own device with fictional practice data.
Existing companion · depth review pendingOpen collection →Read deeply.
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Explore a topic as a collection of learning resources. Choose a chapter, work through a question, inspect the data or return to an explanation.
Explore the SQL reference collection →201 topic collections. Page 7 of 17. Existing companions are not automatically complete study units.
Document and isolate tool environments
Tool Setup & Troubleshooting · Work on your own device with fictional practice data.
Existing companion · depth review pendingOpen collection →Grain
The meaning of one row: order, order line, customer-month or another explicitly defined unit.
Existing companion · depth review pendingOpen collection →Primary key
A field or combination that uniquely identifies a record and is not missing.
Existing companion · depth review pendingOpen collection →Foreign key
A reference to a key in another table; validate unmatched values before trusting the join.
Existing companion · depth review pendingOpen collection →Missing value
A value that is unavailable or unknown; it is not automatically zero or an empty category.
Existing companion · depth review pendingOpen collection →Denominator
The population or exposure count used as the bottom of a ratio.
Existing companion · depth review pendingOpen collection →Baseline
A simple reference method against which a more complex approach is compared.
Existing companion · depth review pendingOpen collection →Data leakage
Information unavailable at the prediction time or improperly crossing evaluation boundaries.
Existing companion · depth review pendingOpen collection →Validation
Explicit checks that data or outputs meet a stated contract.
Existing companion · depth review pendingOpen collection →Reconciliation
Comparing totals or records between sources and transformations, with explained differences.
Existing companion · depth review pendingOpen collection →Aggregation
Combining records into a coarser output grain using defined functions.
Existing companion · depth review pendingOpen collection →One useful next step
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