JDBC ResultSet 存储查询结果失败

Question

我目前正在尝试通过 JDBC 在 Oracle 数据库上运行查询。我已经在 SQLDeveloper 中测试了我的查询，但是当我尝试在我的 Java 程序中运行查询时，我的 ResultSet rs.next() 结果返回 false（意味着 rs 中没有存储任何内容）。

我的代码如下：

public static void testFunction() {
    Properties properties = new Properties();
    properties.put("user", "USERNAMEHERE");
    properties.put("password", "PASSWORDHERE");

    String URL = "jdbc:oracle:thin:@abc:123:def456";
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;
    String sqltxt = "SELECT a.MESSAGE, a.DATE, a.ID_NUM, b.MESSAGE, b.ANOTHER_ID FROM USER.SOME_TABLE_NAME a INNER JOIN USER.DIFFERENT_TABLE_NAME b on a.MESSAGE = b.MESSAGE where a.DATE= '1-December-2014' and b.ANOTHER_ID = 3 and a.ID_NUM IN(0, 100)";


    try {
        conn = DriverManager.getConnection(URL, properties);
        stmt = conn.prepareStatement(sqltxt, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        rs = stmt.executeQuery();
        System.out.println("Records exist? " + rs.next());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try { if (rs != null) rs.close(); } catch (Exception e) {};
        try { if (stmt != null) stmt.close(); } catch (Exception e) {};
        try { if (conn != null) conn.close(); } catch (Exception e) {};
    }
}

我注意到，每当我向 sqltxt 添加 WHERE 子句时，我的 rs.next() 就会产生 false。

感谢任何见解，如果我碰巧自己找到了解决方案，我会在这里发布。

编辑：这是上面相同的代码，但对 sqltxt 的查询不同：

public static void testFunction() {
    Properties properties = new Properties();
    properties.put("user", "USERNAMEHERE");
    properties.put("password", "PASSWORDHERE");

    String URL = "jdbc:oracle:thin:@abc:123:def456";
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;
    String sqltxt = "SELECT MESSAGE FROM USER.SOME_TABLE WHERE DATE = '01-December-2015'";

    try {
        conn = DriverManager.getConnection(URL, properties);
        stmt = conn.prepareStatement(sqltxt, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        rs = stmt.executeQuery();
        System.out.println("Records exist? " + rs.next());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try { if (rs != null) rs.close(); } catch (Exception e) {};
        try { if (stmt != null) stmt.close(); } catch (Exception e) {};
        try { if (conn != null) conn.close(); } catch (Exception e) {};
    }
}

Answer 1

您应该避免在 SQL 文本中使用硬编码的日期。尤其是 Oracle，它需要大量的工作。这里有两个答案，一个使用硬编码日期，另一个正确利用您的PreparedStatement 对象的力量：

在线日期：

public static void testFunction() {
    Properties properties = new Properties();
    properties.put("user", "USERNAMEHERE");
    properties.put("password", "PASSWORDHERE");

    String URL = "jdbc:oracle:thin:@abc:123:def456";
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;
    String sqltxt = "SELECT MESSAGE FROM USER.SOME_TABLE WHERE DATE = to_date('01-December-2015', 'dd-month-yyyy')";

    try (Connection conn = DriverManager.getConnection(URL, properties);
        PreparedStatement stmt = conn.prepareStatement(sqltxt, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        ResultSet rs = stmt.executeQuery();) {

        System.out.println("Records exist? " + rs.next());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

（有关在 Oracle 中硬编码日期的更多信息，请参阅：http://www.techonthenet.com/oracle/functions/to_date.php）

通过参数化 SQL 的日期：

public static void testFunction() {
    Properties properties = new Properties();
    properties.put("user", "USERNAMEHERE");
    properties.put("password", "PASSWORDHERE");

    String URL = "jdbc:oracle:thin:@abc:123:def456";
    String sqltxt = "SELECT MESSAGE FROM USER.SOME_TABLE WHERE DATE = ?";

    try (Connection conn = DriverManager.getConnection(URL, properties);
        PreparedStatement stmt = conn.prepareStatement(sqltxt, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        ResultSet rs = stmt.executeQuery();) {

        stmt.setDate(1, Date.valueOf(LocalDate.now().withYear(2015).withMonth(12).withDayOfMonth(1)));
        System.out.println("Records exist? " + rs.next());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

阅读：http://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html，了解有关在 Java 中使用参数化 SQL 的更多信息。