This is a simple, but helpful example of changing a boolean or bit flag in a table to 'True' when the condition in the subSelect is met. In this context, the SQL statement finds all the cases where a sales agent's email exists in the Metro_SalesForce table and exists in the related table Metro_SalesForceMult. The Metro_SalesForceMult table contains the USA state assignments only for sales agents representing more than a single state.
SET multipleStates = 'True'
WHERE Metro_SalesForce.email in
From Metro_SalesForce x, Metro_SalesForceMult y
Where x.email = y.email