select.java

Java写的含有一个jdbc驱动的小型数据库数据库引擎

     * @throws SQLException
     */
    private void updateAggregateRow(Object row[], Object n[],
				    int len) throws SQLException {
	for (int i = 0; i < len; i++) {
	    int type = eColumn[i].getDataType();

	    switch (eColumn[i].getType()) {

	    case Expression.AVG:

	    case Expression.SUM:

	    case Expression.COUNT:
		row[i] = Column.sum(row[i], n[i], type);

		break;

	    case Expression.MIN:
		row[i] = Column.min(row[i], n[i], type);

		break;

	    case Expression.MAX:
		row[i] = Column.max(row[i], n[i], type);

		break;

	    default:
		row[i] = n[i];

		break;
	    }
	}
    }

    /**
     * Method declaration
     *
     *
     * @param x
     * @param row
     * @param len
     * @param count
     *
     * @throws SQLException
     */
    private void addAggregateRow(Result x, Object row[], int len,
				 int count) throws SQLException {
	for (int i = 0; i < len; i++) {
	    int t = eColumn[i].getType();

	    if (t == Expression.AVG) {
		row[i] = Column.avg(row[i], eColumn[i].getDataType(), count);
	    } else if (t == Expression.COUNT) {

		// this fixes the problem with count(*) on a empty table
		if (row[i] == null) {
		    row[i] = new Integer(0);
		}
	    }
	}

	x.add(row);
    }

    /**
     * Method declaration
     *
     *
     * @param r
     *
     * @return
     *
     * @throws SQLException
     */
    private static Result removeDuplicates(Result r) throws SQLException {
	int len = r.getColumnCount();
	int order[] = new int[len];
	int way[] = new int[len];

	for (int i = 0; i < len; i++) {
	    order[i] = i;
	    way[i] = 1;
	}

	r = sortResult(r, order, way);

	Record n = r.rRoot;

	while (n != null) {
	    Record next = n.next;

	    if (next == null) {
		break;
	    }

	    if (compareRecord(n.data, next.data, r, len) == 0) {
		n.next = next.next;
	    } else {
		n = n.next;
	    }
	}

	return r;
    }

    /**
     * Method declaration
     *
     *
     * @param r
     * @param minus
     *
     * @return
     *
     * @throws SQLException
     */
    private static Result removeSecond(Result r,
				       Result minus) throws SQLException {
	int     len = r.getColumnCount();
	Record  n = r.rRoot;
	Record  last = r.rRoot;
	boolean rootr = true;    // checking rootrecord
	Record  n2 = minus.rRoot;
	int     i = 0;

	while (n != null && n2 != null) {
	    i = compareRecord(n.data, n2.data, r, len);

	    if (i == 0) {
		if (rootr) {
		    r.rRoot = n.next;
		} else {
		    last.next = n.next;
		}

		n = n.next;
	    } else if (i > 0) {    // r > minus
		n2 = n2.next;
	    } else {		   // r < minus
		last = n;
		rootr = false;
		n = n.next;
	    }
	}

	return r;
    }

    /**
     * Method declaration
     *
     *
     * @param r
     * @param r2
     *
     * @return
     *
     * @throws SQLException
     */
    private static Result removeDifferent(Result r,
					  Result r2) throws SQLException {
	int     len = r.getColumnCount();
	Record  n = r.rRoot;
	Record  last = r.rRoot;
	boolean rootr = true;    // checking rootrecord
	Record  n2 = r2.rRoot;
	int     i = 0;

	while (n != null && n2 != null) {
	    i = compareRecord(n.data, n2.data, r, len);

	    if (i == 0) {	      // same rows
		if (rootr) {
		    r.rRoot = n;      // make this the first record
		} else {
		    last.next = n;    // this is next record in resultset
		}

		rootr = false;
		last = n;	      // this is last record in resultset
		n = n.next;
		n2 = n2.next;
	    } else if (i > 0) {       // r > r2
		n2 = n2.next;
	    } else {		      // r < r2
		n = n.next;
	    }
	}

	if (rootr) {		 // if no lines in resultset
	    r.rRoot = null;      // then return null
	} else {
	    last.next = null;    // else end resultset
	}

	return r;
    }

    /**
     * Method declaration
     *
     *
     * @param r
     * @param order
     * @param way
     *
     * @return
     *
     * @throws SQLException
     */
    private static Result sortResult(Result r, int order[],
				     int way[]) throws SQLException {
	if (r.rRoot == null || r.rRoot.next == null) {
	    return r;
	}

	Record source0, source1;
	Record target[] = new Record[2];
	Record targetlast[] = new Record[2];
	int    dest = 0;
	Record n = r.rRoot;

	while (n != null) {
	    Record next = n.next;

	    n.next = target[dest];
	    target[dest] = n;
	    n = next;
	    dest ^= 1;
	}

	for (int blocksize = 1; target[1] != null; blocksize <<= 1) {
	    source0 = target[0];
	    source1 = target[1];
	    target[0] = target[1] = targetlast[0] = targetlast[1] = null;

	    for (dest = 0; source0 != null; dest ^= 1) {
		int n0 = blocksize, n1 = blocksize;

		while (true) {
		    if (n0 == 0 || source0 == null) {
			if (n1 == 0 || source1 == null) {
			    break;
			}

			n = source1;
			source1 = source1.next;
			n1--;
		    } else if (n1 == 0 || source1 == null) {
			n = source0;
			source0 = source0.next;
			n0--;
		    } else if (compareRecord(source0.data, source1.data, r, order, way)
			       > 0) {
			n = source1;
			source1 = source1.next;
			n1--;
		    } else {
			n = source0;
			source0 = source0.next;
			n0--;
		    }

		    if (target[dest] == null) {
			target[dest] = n;
		    } else {
			targetlast[dest].next = n;
		    }

		    targetlast[dest] = n;
		    n.next = null;
		}
	    }
	}

	r.rRoot = target[0];

	return r;
    }
// [e-mail] begin changes from 1.50
    /**
     * Method declaration
     *
     *
     * @param r
     * @param start
     */
  private static void trimResultFront( Result r, int start ) {
    Record n=r.rRoot;
    if(n==null) {
      return;
    }
    while(--start >= 0) {
    	n = n.next;
      if(n == null) {
        return;
      }
	 }
    r.rRoot=n;
  	}
// [e-mail] end changes from 1.50

    /**
     * Method declaration
     *
     *
     * @param r
     * @param maxrows
     */
    private static void trimResult(Result r, int maxrows) {
	Record n = r.rRoot;

	if (n == null) {
	    return;
	}

	while (--maxrows > 0) {
	    n = n.next;

	    if (n == null) {
		return;
	    }
	}

	n.next = null;
    }

    /**
     * Method declaration
     *
     *
     * @param a
     * @param b
     * @param r
     * @param order
     * @param way
     *
     * @return
     *
     * @throws SQLException
     */
    private static int compareRecord(Object a[], Object b[], Result r,
				     int order[],
				     int way[]) throws SQLException {
	int i = Column.compare(a[order[0]], b[order[0]], r.iType[order[0]]);

	if (i == 0) {
	    for (int j = 1; j < order.length; j++) {
		i = Column.compare(a[order[j]], b[order[j]],
				   r.iType[order[j]]);

		if (i != 0) {
		    return i * way[j];
		}
	    }
	}

	return i * way[0];
    }

    /**
     * Method declaration
     *
     *
     * @param a
     * @param b
     * @param r
     * @param len
     *
     * @return
     *
     * @throws SQLException
     */
    private static int compareRecord(Object a[], Object b[], Result r,
				     int len) throws SQLException {
	for (int j = 0; j < len; j++) {
	    int i = Column.compare(a[j], b[j], r.iType[j]);

	    if (i != 0) {
		return i;
	    }
	}

	return 0;
    }

}