public R as(Expression<?> expr) {
        Expression<?> flag = ExpressionUtils.operation(alias.getType(), SQLOps.WITH_ALIAS, alias, expr);
        return queryMixin.addFlag(new QueryFlag(QueryFlag.Position.WITH, flag));
    }
{@code WithBuilder} is a builder for common table expressions

@author tiwe

@param <R>
querydsl-sql/src/main/java/com/querydsl/sql/WithBuilder.java