计数删除的记录，returns 0

Question

我通过调用方法 action.deleteBox(box); 从我的 servlet 在我的 table 中执行一个 DELETE，该方法执行删除函数

删除框方法

Connection c = null;
PreparedStatement stm = null;
sq = "DELETE FROM BOXES WHERE ...";

try {       
    Class.forName(typeDB);
    c = DriverManager.getConnection(path);    
    stm = c.prepareStatement(sq);
    //...
    stm.executeUpdate();

} catch (SQLException e) {             
    System.out.println(e.getMessage());
} finally {
        System.out.println("my stm is closed : " + stm.isClosed());
        if (stm != null)
                    stm.close();
        if (c != null)
                    c.close();
}

删除执行正常。然后我想查看之前delete删除了多少条记录：所以我调用这个方法：

public int countDeletesRecords() 
        throws SQLException, ClassNotFoundException {

    Connection c = null;
    PreparedStatement stm = null;
    sq = "SELECT changes() as \"deletedRows\" ";
    int deletedRows=-1;

    try {       
        Class.forName(typeDB);
        c = DriverManager.getConnection(path);    
        stm = c.prepareStatement(sq);       
        ResultSet rs = stm.executeQuery();

        if (rs.next()) {
            deletedRows = rs.getInt("deletedRows");
        }

    } catch (SQLException e) {             
        System.out.println(e.getMessage());
    } finally {
        System.out.println("my stm is closed : " + stm.isClosed());
        if (stm != null)
            stm.close();
        if (c != null)
            c.close();
    } 

    return deletedRows; //I get 0..
}

我得到 0 条记录，而 1 条记录被删除。

Answer 1

虽然这不能直接回答问题，但另一种更简单的方法是捕获 executeUpdate() 的 return 值，即 return 受影响的人数（在本例中, 删除) 行:

final int deletedRowCount = stm.executeUpdate();

Answer 2

documentation 说：

This function returns the number of rows modified, inserted or deleted by the most recently completed INSERT, UPDATE or DELETE statement on the database connection

您正在创建一个新的数据库连接，其中从未执行过任何 DELETE 语句。

计数删除的记录，returns 0

Count deleted records, returns 0

sqlite

jdbc

prepared-statement