Uniqueness
Whether each real thing appears only once in a dataset: one row per customer, and no order number used twice.
Uniqueness can be checked exactly on a key and only approximately on the thing itself. Two rows with different IDs can still describe the same person.
Where it comes up
- Exact duplicate rowsThe same row appears more than once, identical in every column.
- Near-duplicate recordsTwo rows describe the same real thing but differ enough that an exact comparison misses them.
- Duplicate keys with conflicting valuesTwo rows share an identifier that should be unique, but disagree on other fields.
See also
- DuplicateA record that describes the same real thing as another record in the same dataset. An exact duplicate matches in every field; a near duplicate differs in spelling, format, or detail.
- Primary keyA column, or set of columns, whose value is unique for every row and identifies it: a customer number, an order ID.
- DeduplicationFinding records that describe the same real thing and reducing them to one.