/**
* Applies a mapping to a field collation.
*
* <p>If the field is not mapped, returns null.
*
* @param mapping Mapping
* @param fieldCollation Field collation
* @return collation with mapping applied
*/
public static RelFieldCollation apply(
Mappings.TargetMapping mapping, RelFieldCollation fieldCollation) {
final int target = mapping.getTargetOpt(fieldCollation.getFieldIndex());
if (target < 0) {
return null;
}
return fieldCollation.copy(target);
}
@Override
public RexNode visitInputRef(RexInputRef local) {
final int index = local.getIndex();
int target = mapping.getTarget(index);
return new RexInputRef(target, local.getType());
}