/**
* 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);
}
/** Converts a collation to an ORDER BY item. */
public SqlNode toSql(RelFieldCollation collation) {
SqlNode node = field(collation.getFieldIndex());
switch (collation.getDirection()) {
case DESCENDING:
case STRICTLY_DESCENDING:
node = SqlStdOperatorTable.DESC.createCall(POS, node);
}
switch (collation.nullDirection) {
case FIRST:
node = SqlStdOperatorTable.NULLS_FIRST.createCall(POS, node);
break;
case LAST:
node = SqlStdOperatorTable.NULLS_LAST.createCall(POS, node);
break;
}
return node;
}