idcols

Idcols, short for identifier columns, is a term used in data processing to denote the subset of columns that uniquely identify a row within a dataset. In practice, idcols may correspond to a database primary key, a composite key formed from multiple columns, or a set of attributes chosen to serve as stable identifiers across data transformations.

Idcols are used in tasks such as joining, merging, deduplicating, or upserting records, where matching is performed based on the values of these columns rather than on the entire row. In analytic pipelines, idcols help maintain referential integrity when data are reshaped or augmented. Depending on the system, idcols can be declared explicitly by users or inferred by the tool from the data, and they may be required to be non-nullable or unique.

Implementation varies: In SQL databases, the role of idcols is played by primary keys or unique constraints; in data processing frameworks, a parameter named idcols may specify which fields constitute the key for row identification. Composite idcols combine multiple fields, for example (country, year, product_id) acting as an identifier for a given product in a given country and year.

Considerations include changes to the identified columns that can affect data lineage, missing values that complicate matching, and performance implications that depend on indexing and key stability. In some workflows, natural keys are replaced with surrogate ids to improve reliability and speed.

See also: primary key, composite key, surrogate key, deduplication.