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When a single column is marked IsExtractionIdentifier RDMP will use this column for building cohorts. When two or more columns are marked IsExtractionIdentifier (e.g. Mother CHI, baby CHI for a Maternity dataset) then you must choose which column to use.
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When adding a dataset with multiple IsExtractionIdentifier columns to a CohortIdentificationConfiguration you will be prompted to pick which column to pull identifiers from. Since cohort building in RDMP is based on set operations (UNION , INTERSECT etc) it is not possible to select two columns at once for a given set.
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When extracting a dataset in an ExtractionConfiguration RDMP performs a JOIN on a cohort table. The cohort table stores the Release identifier for all Private identifiers in the cohort. For example:
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