order_col.ascending = !descending;
m_aggregationList.clear();
AbstractExpression order_exp = parseExpressionTree(child);
assert(order_exp != null);
if (isDistributed) {
order_exp = order_exp.replaceAVG();
updateAvgExpressions();
}
order_col.expression = order_exp;
ExpressionUtil.finalizeValueTypes(order_col.expression);