Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 3)
     Function multiply (children 1)
      ExpressionList (children 2)
       Function avg (children 1)
        ExpressionList (children 1)
         Identifier b
       Literal UInt64_3
     Function plus (children 1)
      ExpressionList (children 2)
       Function plus (children 1)
        ExpressionList (children 2)
         Function sum (children 1)
          ExpressionList (children 1)
           Identifier b
         Literal UInt64_1
       Function count (children 1)
        ExpressionList (children 1)
         Identifier b
     Function multiply (children 1)
      ExpressionList (children 2)
       Function count (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 b
           TablesInSelectQuery (children 1)
            TablesInSelectQueryElement (children 1)
             TableExpression (children 1)
              TableIdentifier fuse_tbl