@Override
 public void meet(SqlLowerCase node) throws RuntimeException {
   super.meet(node);
   if (node.getArg() instanceof SqlNull) {
     replace(node, new SqlNull());
   } else if (node.getArg() instanceof SqlConstant) {
     SqlConstant arg = (SqlConstant) node.getArg();
     String lower = arg.getValue().toString().toLowerCase(Locale.US);
     replace(node, str(lower));
   }
 }
 @Override
 public void meet(SqlEq node) throws RuntimeException {
   super.meet(node);
   SqlExpr left = node.getLeftArg();
   SqlExpr right = node.getRightArg();
   if (left instanceof SqlNull || right instanceof SqlNull) {
     replace(node, new SqlNull());
   } else if (left instanceof SqlConstant<?> && right instanceof SqlConstant<?>) {
     SqlConstant<?> l = (SqlConstant<?>) left;
     SqlConstant<?> r = (SqlConstant<?>) right;
     if (l.getValue().equals(r.getValue())) {
       replace(node, new TrueValue());
     } else {
       replace(node, new FalseValue());
     }
   }
 }