for (Ordering od : orderings) {
// first, we rewrite the evaluation stack for each side of the comparison.
ErrorCollector collector = new ErrorCollectorImpl();
final LogicalExpression expr = ExpressionTreeMaterializer.materialize(od.getExpr(), batch, collector, context.getFunctionRegistry());
if (collector.hasErrors()) {
throw new SchemaChangeException("Failure while materializing expression. " + collector.toErrorString());
}
g.setMappingSet(leftMapping);
HoldingContainer left = g.addExpr(expr, false);
g.setMappingSet(rightMapping);
HoldingContainer right = g.addExpr(expr, false);