Explain EXPLAIN (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 3)
    ExpressionList (children 1)
     Asterisk
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier users (alias u1)
    Function equals (children 1)
     ExpressionList (children 2)
      Identifier uid
      Subquery (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 1)
         SelectQuery (children 3)
          ExpressionList (children 1)
           Function sum (children 1)
            ExpressionList (children 1)
             Identifier age
          TablesInSelectQuery (children 1)
           TablesInSelectQueryElement (children 1)
            TableExpression (children 1)
             TableIdentifier users (alias u2)
          Function equals (children 1)
           ExpressionList (children 2)
            Identifier u1.name
            Identifier u2.name
