Question

我有以下代码：

try {
    String sql = "SELECT COUNT(*) AS \"Jumlah\" FROM dokter";
    ResultSet rs = connection.st.executeQuery(sql);

    if(rs.next()){ 
        abc = rs.getString("Jumlah").toString();    
    }
} catch (Exception e) {
    System.out.println("\n Message: " + e.getMessage());
}

为什么我的ResultSet无法执行给定的SQL？

Answer 1

丢失别名，这只是一个不必要的并发症。只需通过列索引引用ResultSet：

try {
    String sql = "SELECT COUNT(*) FROM dokter";
    ResultSet rs = connection.st.executeQuery(sql);

    if(rs.next()) { 
        abc = rs.getInt(1); // or getString(1) if you need it as a String    
    }
} catch (Exception e) {
    System.out.println("\n Message: " + e.getMessage());
}

Answer 2

我建议您使用PreparedStatement和try-with-resources关闭它（以及您的ResultSet）。 count不是String，如果您有Connection connection，那么您可以执行类似

的操作

int count = 0;
try {
    String sql = "SELECT COUNT(*) FROM dokter";
    try (PreparedStatement ps = connection.prepareStatement(sql);
            ResultSet rs = ps.executeQuery()) {
        if (rs.next()) {
            count = rs.getInt(1);
        }
    }
} catch (Exception e) {
    e.printStackTrace();
} finally {
    if (connection != null) {
        try {
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

使用Java和Netbeans从我的数据库中选择计数

2 个答案: