# Selectors and Matchers — Prometheus + Grafana

Source: https://www.skillbyai.com/en/prometheus-grafana/q-select

> Instant and range vectors.

## Pick series by name and labels

A selector such as `http_requests_total{job="orders-api", status=~"5.."}` returns matching series. Label matchers are `=`, `!=`, `=~` (regex match) and `!~` (regex non-match). An **instant vector** has one sample per series at the evaluation time; adding a duration in brackets, as in `[5m]`, gives a **range vector** with all samples in that window, which functions like `rate` need. `offset 1h` shifts the window back for comparisons.

## Asking questions of time series

Selectors, rate functions and aggregation answer most monitoring questions.

![Three ideas: selectors, rates, aggregation.](assets/figures/prometheus-grafana/section-4-map.svg) — Figure 4.1 — Selectors, rates and aggregation.

## Selector examples

PromQL.

```promql
# all 5xx responses of the orders API (instant vector)
http_requests_total{job="orders-api", status=~"5.."}

# last 5 minutes of samples (range vector, input to rate())
http_requests_total{job="orders-api"}[5m]

# targets that are down
up == 0

# the same series one day ago
http_requests_total{job="orders-api"} offset 1d
```

## Regex matchers are fully anchored

status=~"5.." matches 500 to 599 but not 1500, because PromQL regexes match the whole value.

**Quiz:** Which matcher selects labels matching a regular expression?

- [x] =~
- [ ] ==
- [ ] !=
- [ ] ~~

*Answer:* =~. !~ is the negated form.