Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 2)
     Identifier key
     Identifier a
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier test
    ExpressionList (children 3)
     OrderByElement (children 1)
      Identifier key
     OrderByElement (children 1)
      Identifier a
     OrderByElement (children 1)
      Function exp (children 1)
       ExpressionList (children 1)
        Function plus (children 1)
         ExpressionList (children 2)
          Identifier key
          Identifier a
    Set
