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I have run into a couple of problems while trying to convert an existing JDBC application to use HSQLDB version 2.2.9 (Currently the codebase runs successfully on MySQL, ORACLE and SQLServer, but an embedded database seemed like a good option too).

I will ask the questions one at a time and separately (although they all relate to the JDBC ResultSet.deleteRow() method, supported since HSQLDB 2.0)

Why does rs.next() return false after calling rs.deleteRow()?

Here is a complete self contained code sample (including simple table creation, sample inserts, and deleting the table at the end):

    int deletedRows=0;
    try{
        Connection c = DriverManager.getConnection("jdbc:hsqldb:mem:mytestdb",
                 "SA", "");
        String createSQL =
                 "create table test (num INTEGER PRIMARY KEY, str VARCHAR(25))";
        Statement createStmt = c.createStatement();
        createStmt.execute(createSQL);
        createStmt.close();
        String ins = "insert into test (num,str) values (?,?)";
        PreparedStatement pStmt = c.prepareStatement(ins);
        for(int i=0; i<100; i++){
            pStmt.setInt(1, i);
            pStmt.setString(2, "String"+i);
            pStmt.execute();
        }
        // there should now be 100 rows in the table
        String select = "SELECT * FROM test";
        PreparedStatement stmt = c.prepareStatement(select, 
                ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
        ResultSet rs = stmt.executeQuery();    
        rs.beforeFirst();
        while(rs.next()){
            int num = rs.getInt("num");
            if((num%7)==0){
                System.out.println("Deleting row:"+num);
                rs.deleteRow();
                deletedRows++;
            }
        }
        Statement dropStmt = c.createStatement();
        dropStmt.execute("drop table test;");
        dropStmt.close();
    } catch (SQLException sqle) {
        System.out.println("Deleted "+deletedRows+
                    " rows before exception: "+sqle.getMessage());
        sqle.printStackTrace();
    }

When running the same code on MySQL database, the output shows that every 7th row is deleted:

Deleting row:0

Deleting row:7

...

Deleting row: 98

On HSQLDB, the output is:

Deleting row:0

The rs.next() returns false after the first call to rs.deleteRow().

I cannot find any information in the HSQLDB javadoc. Does anyone have any ideas?

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3 回答 3

1

Specify the cursor holdability in the code:

c.prepareStatement(select,
     ResultSet.TYPE_SCROLL_INSENSITIVE,
     ResultSet.CONCUR_UPDATABLE,
     ResultSet.HOLD_CURSORS_OVER_COMMIT);

The problem seems to be that HSQLDB JDBC driver uses ResultSet.CLOSE_CURSORS_AT_COMMIT as the default value.

于 2013-03-05T11:36:12.230 回答
1

正如我之前评论过的，这听起来像是 HSQLDB JDBC 实现中的一个错误。JDBC 4.1 规范（第 15.2.4.2 节）说：

调用该方法后deleteRow，光标将定位在下一个有效行之前。如果删除的行是最后一行，则光标将定位在最后一行之后。

这意味着调用next()应该已经返回true（如果ResultSet包含更多行）。

于 2013-03-02T07:57:50.160 回答
0

最有可能的是，您的配置错误。例如，您的类路径中可能有旧版本的 HSQLDB jar。

我用当前的 SVN 代码得到这个输出。自 2.2.9 以来，JDBC 代码没有改变。

Deleting row:0
Deleting row:7
Deleting row:14
Deleting row:21
Deleting row:28
Deleting row:35
Deleting row:42
Deleting row:49
Deleting row:56
Deleting row:63
Deleting row:70
Deleting row:77
Deleting row:84
Deleting row:91
Deleting row:98
于 2013-03-03T20:17:24.583 回答