/**
* Returns the tuple descriptor (schema) of the specified table
*
* @param tableid The id of the table, as specified by the DbFile.getId() function passed to
* addTable
* @throws NoSuchElementException if the table doesn't exist
*/
public TupleDesc getTupleDesc(int tableid) throws NoSuchElementException {
// some code goes here
String fileName = fileId.get(tableid);
if (fileName.equals(null)) throw new NoSuchElementException();
DbFile retTD = tableFile.get(fileName);
if (retTD.equals(null)) throw new NoSuchElementException();
// System.out.println(retTD);
else return retTD.getTupleDesc();
}
/**
* Create a new TableStats object, that keeps track of statistics on each column of a table
*
* @param tableid The table over which to compute statistics
* @param ioCostPerPage The cost per page of IO. This doesn't differentiate between
* sequential-scan IO and disk seeks.
*/
public TableStats(int tableid, int ioCostPerPage) {
// For this function, we use the DbFile for the table in question,
// then scan through its tuples and calculate the values that you
// to build the histograms.
// TODO: Fill out the rest of the constructor.
// Feel free to change anything already written, it's only a guideline
this.ioCostPerPage = ioCostPerPage;
DbFile file = Database.getCatalog().getDbFile(tableid);
tupleDesc = file.getTupleDesc();
numPages = ((HeapFile) file).numPages();
numTuples = 0;
int numFields = tupleDesc.numFields();
// TODO: what goes here?
statistics = new ArrayList<Object>();
for (int i = 0; i < numFields; i++) {
if (Type.INT_TYPE.equals(tupleDesc.getFieldType(i))) {
statistics.add(new IntStatistics(NUM_HIST_BINS));
} else {
statistics.add(new StringHistogram(NUM_HIST_BINS));
}
}
final DbFileIterator iter = file.iterator(null);
try {
iter.open();
while (iter.hasNext()) {
Tuple t = iter.next();
numTuples++;
// TODO: and here?
for (int i = 0; i < numFields; i++) {
if (Type.INT_TYPE.equals(tupleDesc.getFieldType(i))) {
((IntStatistics) statistics.get(i)).addValue(((IntField) t.getField(i)).getValue());
} else {
((StringHistogram) statistics.get(i))
.addValue(((StringField) t.getField(i)).getValue());
}
}
}
iter.close();
} catch (DbException e) {
e.printStackTrace();
} catch (TransactionAbortedException e) {
e.printStackTrace();
}
}