[英]JDBC ResultSet fails to store query results
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中测试了查询,但是当我尝试在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,每当我在sqltxt中添加WHERE子句时,即rs.next()产生false时。
感谢您提供任何见识,如果我碰巧自己找到解决方案,我将在此处发布。
编辑:这是来自BUT的相同代码,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) {};
}
}
您应该避免在SQL文本中使用硬编码的日期。 特别是对于Oracle,它需要大量工作。 这是两个答案,一个答案使用硬编码日期,另一个答案正确利用了PreparedStatement
对象的功能:
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Oracle中硬编码日期的更多信息,请参见: 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();
}
}
请阅读: http : //docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html ,以获取有关在Java中使用参数化SQL的更多信息。
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