Seeking help with Prometheus empty value problem

[张星]

When the value of query_result_sys_network_track_error is empty, the result is also empty. I want it to default to 0, regardless of whether the minuend or subtrahend is empty. I tried using vector(0), but when used together with sum by, the same problem occurs.

My current query is:

```

(sum by (host)(sum_over_time(query_result_sys_network_track_error[24h]))) - (sum by (host)(sum_over_time(query_result_sys_network_track_error[24h] offset 7d)))

```

I tried using vector(0) to solve this problem but it did not work:

```

(sum by (host)(sum_over_time(query_result_sys_network_track_error)) or vector(0)) - (sum by (host)(sum_over_time(query_result_sys_network_track_error[24h] offset 7d)) or vector(0))

```