private QueryBlockInfo convertSource(RelNode r) {
Schema s;
ASTNode ast;
if (r instanceof TableAccessRelBase) {
TableAccessRelBase f = (TableAccessRelBase) r;
s = new Schema(f);
ast = ASTBuilder.table(f);
} else if (r instanceof JoinRelBase) {
JoinRelBase join = (JoinRelBase) r;
QueryBlockInfo left = convertSource(join.getLeft());