Union three sources

Hey all!  Struggling a bit here...  Why doesnt this work?

let
  UAT = Sql.Database("uat-sqlserver.database.windows.net", "uat-operation-db", [Query="
    select 'UAT' [Environment], Id, GroupId, Name from Customers where EnableBiDashboard = 1 
  "]),
  RC = Sql.Database("uat-sqlserver.database.windows.net", "rc-operation-db", [Query="
    select 'RC' [Environment], Id, GroupId, Name from Customers where EnableBiDashboard = 1 
  "]),
  PROD = Sql.Database("prod-sqlserver.database.windows.net", "prod-operation-db", [Query="
    select 'PROD' [Environment], Id, GroupId, Name from Customers  where EnableBiDashboard = 1 
  "]),
  Source = Table.Combine({ UAT,RC,PROD})
in
  Source