SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 3)
    Function uniq (alias a) (children 1)
     ExpressionList (children 1)
      Identifier user_id
    Function min (alias x) (children 1)
     ExpressionList (children 1)
      Identifier _sample_factor
    Function multiply (children 1)
     ExpressionList (children 2)
      Identifier a
      Identifier x
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 2)
      TableIdentifier sessions
      SampleRatio 10000000
