public C addFlag(Position position, Expression<?> flag) {
        metadata.addFlag(new QueryFlag(position, flag));
        return (C) this;
    }
Add the given Expression at the given position as a query flag

@param position position
@param flag query flag
@return the current object
querydsl-sql/src/main/java/com/querydsl/sql/dml/AbstractSQLUpdateClause.java