Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 2)
     Function sum (children 1)
      ExpressionList (children 1)
       Identifier b
     Function count (children 1)
      ExpressionList (children 1)
       Identifier b
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       Subquery (children 1)
        SelectWithUnionQuery (children 1)
         ExpressionList (children 1)
          SelectQuery (children 2)
           ExpressionList (children 1)
            Identifier x (alias b)
           TablesInSelectQuery (children 1)
            TablesInSelectQueryElement (children 1)
             TableExpression (children 1)
              Subquery (children 1)
               SelectWithUnionQuery (children 1)
                ExpressionList (children 1)
                 SelectQuery (children 2)
                  ExpressionList (children 2)
                   Function sum (alias x) (children 1)
                    ExpressionList (children 1)
                     Identifier b
                   Function count (children 1)
                    ExpressionList (children 1)
                     Identifier b
                  TablesInSelectQuery (children 1)
                   TablesInSelectQueryElement (children 1)
                    TableExpression (children 1)
                     TableIdentifier fuse_tbl