Обсуждение: JDBC3 and 7.4.1

On Fri, 20 Feb 2004, Ranjeet Kapur wrote:

> Hi,
>
>              ResultSet rs = select_stmnt.executeQuery(query);
>              System.out.println("Select Size = " + rs.getFetchSize());
>              num_entries = rs.getFetchSize();
>

getFetchSize does not return the number of result rows.  It did prior to
7.4, but that was just an implementation artifact and should not have been
relied on.

Kris Jurka

Ranjeet Kapur wrote:
> Thanks, I just did a few experiments and  found the same thing, that
> getFetchSize() was returning 0. Is there anything else I could use to
> achieve the same result, namely how many rows in the select ?? I am very
> new to DB programming that´s why I probably misread the documentation on
> getFetchSize().

Add a COUNT(*) to the query, if you can; then the count will appear as a
column in your resultset.

Alternatively:

   Statement stmt =
connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
   ResultSet rs = stmt.executeQuery(query);

   // Count rows.
   rs.last();
   int resultSetSize = rs.getRow();

   // Process actual resultset
   rs.beforeFirst();
   while (rs.next()) {
     // do stuff
   }

but this requires iterating over the resultset twice, and using
TYPE_SCROLL_INSENSITIVE prevents the current driver from using cursors
to incrementally fetch data, so you will have the entire resultset in
memory on the Java side.

If you don't need the total count before processing the resultset, just
count as you process each result row (then you don't need a
TYPE_SCROLL_INSENSITIVE ResultSet, either).

-O