/**
* This is used to compute the predicate or value columns in the PH tables Deals with multiple
* hash functions
*
* @param columnName
* @return
*/
private String hashColumnExpression(String columnName) {
String predicateString = planNode.getTriple().getPredicate().toString();
PredicateTable hashingFamily = null;
AccessMethod am = planNode.getMethod();
if (AccessMethodType.isDirectAccess(am.getType())) {
hashingFamily = store.getDirectPredicates();
} else {
hashingFamily = store.getReversePredicates();
}
int numberOfPredHashes = hashingFamily.getHashCount(predicateString);
if (numberOfPredHashes == 0) {
return null;
} else if (numberOfPredHashes
== 1 /*&& (mergeLogicType != SQLLogicNodeType.AND || !tapn.hasPossibleSpills(store))*/) {
String pExpression = "T." + columnName + hashingFamily.getHashes(predicateString)[0];
return pExpression;
} else {
MonitoredStringBuffer tmpProjectString = new MonitoredStringBuffer(" CASE ");
for (int h = 0; h < numberOfPredHashes; h++) {
int hash = hashingFamily.getHashes(predicateString)[h];
if (hash == -1) {
hash = 0;
}
readPredicateColumn(predicateString, tmpProjectString, hash, columnName);
if (hashingFamily.getHashes(predicateString)[0] == -1) {
break;
}
}
tmpProjectString.append(" ELSE NULL END");
return tmpProjectString.toString();
}
}
private void readPredicateColumn(
String predicateString, MonitoredStringBuffer projectString, int hash, String columnName) {
projectString.append(" WHEN T.");
projectString.append(Constants.NAME_COLUMN_PREFIX_PREDICATE);
projectString.append(hash);
projectString.append(" = '");
projectString.append(printPredicateString(predicateString));
projectString.append("' ");
projectString.append(" THEN T.");
projectString.append(columnName);
projectString.append(hash);
projectString.append("\n");
}