为某些索引迭代并从JSON获取唯一值

Question

我使用如下查询从PHP中获取数据：

SELECT objective,signal_type,signal_name FROM signals WHERE channel="Email"

数据是这样返回的：

[
    {
        "objective": "Awareness",
        "signal_type": "Efficiency",
        "signal_name": "CPM"
    },
    {
        "objective": "Awareness",
        "signal_type": "Quality",
        "signal_name": "Click-thru Rate"
    },
    {
        "objective": "Awareness",
        "signal_type": "Quality",
        "signal_name": "Frequency"
    },
    {
        "objective": "Awareness",
        "signal_type": "Quality",
        "signal_name": "Interaction Rate"
    },
    {
        "objective": "Awareness",
        "signal_type": "Quality",
        "signal_name": "Viewability"
    },
    {
        "objective": "Awareness",
        "signal_type": "Volume",
        "signal_name": "Display Time"
    },
    {
        "objective": "Awareness",
        "signal_type": "Volume",
        "signal_name": "Impression"
    },
    {
        "objective": "Awareness",
        "signal_type": "Volume",
        "signal_name": "Reach"
    },
    {
        "objective": "Conversion",
        "signal_type": "Efficiency",
        "signal_name": "Cost per Action"
    },
    {
        "objective": "Conversion",
        "signal_type": "Efficiency",
        "signal_name": "ROI/ROAS"
    },
    {
        "objective": "Conversion",
        "signal_type": "Quality",
        "signal_name": "Avg Order Value"
    },
    {
        "objective": "Conversion",
        "signal_type": "Volume",
        "signal_name": "Conversion"
    },
    {
        "objective": "Conversion",
        "signal_type": "Volume",
        "signal_name": "Revenue"
    },
    {
        "objective": "Engagement",
        "signal_type": "Efficiency",
        "signal_name": "Cost per Click"
    },
    {
        "objective": "Engagement",
        "signal_type": "Quality",
        "signal_name": "Avg Interaction Time"
    },
    {
        "objective": "Engagement",
        "signal_type": "Quality",
        "signal_name": "Conversion Rate"
    },
    {
        "objective": "Engagement",
        "signal_type": "Volume",
        "signal_name": "Click"
    },
    {
        "objective": "Engagement",
        "signal_type": "Volume",
        "signal_name": "Interaction"
    },
    {
        "objective": "Engagement",
        "signal_type": "Volume",
        "signal_name": "Interaction Time"
    }
]

我可以将这一切附加到一个表中，如下所示：

$.each(data, function(index, key) {
 $('#myTable').append('<tr><td>'+key.objective+'</td><td>'+key.signal_type+'</td><td>'+key.signal_name+'</td></tr>');
                });

这会产生一个非常准确的表格，但不是一个美观的表格。我得到的东西是这样的：

| Signal Type | Signal Types | Available Signals    |
|-------------|--------------|----------------------|
| Awareness   | Efficiency   | CPM                  |
| Awareness   | Quality      | Click-thru Rate      |
| Awareness   | Quality      | Frequency            |
| Awareness   | Quality      | Interaction Rate     |
| Awareness   | Quality      | Viewability          |
| Awareness   | Volume       | Display Time         |
| Awareness   | Volume       | Impression           |
| Awareness   | Volume       | Reach                |
| Conversion  | Efficiency   | Cost per Action      |
| Conversion  | Efficiency   | ROI/ROAS             |
| Conversion  | Quality      | Avg Order Value      |
| Conversion  | Volume       | Conversion           |
| Conversion  | Volume       | Revenue              |
| Engagement  | Efficiency   | Cost per Click       |
| Engagement  | Quality      | Avg Interaction Time |
| Engagement  | Quality      | Conversion Rate      |
| Engagement  | Volume       | Click                |
| Engagement  | Volume       | Interaction          |
| Engagement  | Volume       | Interaction Time     |

(请注意，标题在我的HTML中是“硬编码”的)

我理想中想要的是这样的东西：

| Signal Type | Signal Types | Available Signals    |
|-------------|--------------|----------------------|
| Awareness   | Efficiency   | CPM                  |
|             | Quality      | Click-thru Rate      |
|             |              | Frequency            |
|             |              | Interaction Rate     |
|             |              | Viewability          |
|             | Volume       | Display Time         |
|             |              | Impression           |
|             |              | Reach                |
| Conversion  | Efficiency   | Cost per Action      |
|             |              | ROI/ROAS             |
|             | Quality      | Avg Order Value      |
|             | Volume       | Conversion           |
|             |              | Revenue              |
| Engagement  | Efficiency   | Cost per Click       |
|             | Quality      | Avg Interaction Time |
|             |              | Conversion Rate      |
|             | Volume       | Click                |
|             |              | Interaction          |
|             |              | Interaction Time     |

这里的区别在于，根据之前的列，列中有不同的值。你对如何得到这个输出有什么想法吗？请注意，我可以根据效率最高的选项来调整我的SQL查询或javascript/jquery (或两者)。