discrepancy in montherapy query

[clarkevans]

For the mono-therapy query in the cohort query, this is using the drug_exposure table rather than the drug_era table. The problem with using the drug exposure table directly is that it will exclude individuals who happen to have 2 records that provide exact same drug. It seems like this would need to be collapsed, and that's what the drug_era table does. The generated SQL uses the drug_era table when computing this particular condition.