protected void visit(SelectStmt s) throws VisitException {
List<AliasedExpr> exprs = s.getSelectExprs();
for (int i = 0; i < exprs.size(); i++) {
AliasedExpr e = exprs.get(i);
before(s, e);
e.accept(this);
after(s, e);
}
before(s, s.getSource());
s.getSource().accept(this);