SQLite ExecuteQuery使用Java非常慢（NetBeans）

Question

I use sqlite to store data. I am trying to get data from sqlite table view and fill array of objects in java, but Query Execution takes very long time. I only have 32 objects with 22 fields, and sqlite with 380 rows. But to Execute similar statement took me 17 seconds for 32 objects.

 sql = "SELECT "
                        + "           field1,"
                        + "           field2,"
                        ....
                        + "           field22"
                        + " from Rankedview WHERE Ranking = " + Integer.toString(RankingIndex);
 try (ResultSet rs = stmt.executeQuery(sql)) {
                    while (rs.next()) {
                        a[j].field1= rs.getString("field1");
                        ..........
                        a[j].field22 = rs.getInt("field22");
                    }

                }

After I updated sqlite-jdbc driver from 3.7.2 to 3.8.5 time from 17 seconds lowered to 9 seconds.

How can I improve its performance?

Edit:

view definition (ATP is a table)

CREATE VIEW Ranked AS
SELECT p1.ID,
       p1.field2,
       ...

       p1.field21,
       (
           SELECT count() + (
                                SELECT count() + 1
                                  FROM Table AS p2
                                 WHERE p2.field21 = p1.field21 AND 
                                       p2.id > p1.id
                            )
             FROM ATP AS p2
            WHERE p2.field21 > p1.field21
       )
       AS Ranking
  FROM ATP AS p1
 ORDER BY Ranking ASC;

EXPLAIN QUERY PLAN output:

selectid order from detail
0   0   0   SCAN TABLE ATP AS p1
0   0   0   EXECUTE CORRELATED SCALAR SUBQUERY 1
1   0   0   SCAN TABLE ATP AS p2
1   0   0   EXECUTE CORRELATED SCALAR SUBQUERY 2
2   0   0   SEARCH TABLE ATP AS p2 USING INTEGER PRIMARY KEY (rowid>?)
0   0   0   EXECUTE CORRELATED SCALAR SUBQUERY 3
3   0   0   SCAN TABLE ATP AS p2
3   0   0   EXECUTE CORRELATED SCALAR SUBQUERY 4
4   0   0   SEARCH TABLE ATP AS p2 USING INTEGER PRIMARY KEY (rowid>?)
0   0   0   EXECUTE CORRELATED SCALAR SUBQUERY 5
5   0   0   SCAN TABLE ATP AS p2
5   0   0   EXECUTE CORRELATED SCALAR SUBQUERY 6
6   0   0   SEARCH TABLE ATP AS p2 USING INTEGER PRIMARY KEY (rowid>?)
0   0   0   USE TEMP B-TREE FOR ORDER BY

Answer 1

To get a row with a specific rank, you should not compute the rank by hand, but use the LIMIT/OFFSET clauses :

SELECT ...
FROM ATP
ORDER BY field21, id
LIMIT 1 OFFSET x

This still requires sorting all table rows to determine which is the x-th, but is much more efficient than multiple nested table scans.