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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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When extracting a dataset with multiple IsExtractionIdentifier columns (e.g. see below) all private identifiers will be removed. Where the private identifier exists in the cohort it will be substituted for the Release Identifier. If it does not exist then it will be substituted for null. This allows you to build a cohort based on Mothers or Children.
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