# Indexes

During data transfer, indexes are created on the following tables.

Columns that are indexed during data transfer

Table | Columns on which indexes are created
--- | ---
PERSON | PATIENT_ID
DRUG_ERA | PATIENT_ID DRUG_ERA_START_DATE DRUG_CONCEPT_ID
DRUG_EXPOSURE | PATIENT_ID DRUG_EXPOSURE_START_DATE DRUG_CONCEPT_ID
CONDITION_ERA | PATIENT_ID CONDITION_ERA_START_DATE CONDITION_CONCEPT_ID
CONDITION_OCCURRENCE | PATIENT_ID CONDITION_START_DATE CONDITION_CONCEPT_ID
PROCEDURE_OCCURRENCE | PATIENT_ID PROCEDURE_DATE PROCEDURE_CONCEPT_ID

The transformation process creates additional single-column indexes, one for each configuration variable, based on a column that exists in the base tables.

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