> NOTE: If you're not seeing the `Data Sources` link in your side menu it means that your current user does not have the `Admin` role for the current organization.
group by time you need an aggregation function. Some functions like derivative require an aggregation function. The editor tries simplify and unify this part of the query. For example:<br>
- $tag_exampletag = replaced with the value of the `exampletag` tag. The syntax is `$tag_yourTagName` (must start with `$tag_`). To use your tag as an alias in the ALIAS BY field then the tag must be used to group by in the query.
- You can also use [[tag_hostname]] pattern replacement syntax. For example, in the ALIAS BY field using this text `Host: [[tag_hostname]]` would substitute in the `hostname` tag value for each legend value and an example legend value would be: `Host: server1`.
Instead of hard-coding things like server, application and sensor name in you metric queries you can use variables in their place.
Variables are shown as dropdown select boxes at the top of the dashboard. These dropdowns makes it easy to change the data
being displayed in your dashboard.
Checkout the [Templating]({{< relref "reference/templating.md" >}}) documentation for an introduction to the templating feature and the different
types of template variables.
### Query variable
If you add a template variable of the type `Query` you can write a InfluxDB exploration (meta data) query. These queries can
return things like measurement names, key names or key values.
For example you can have a variable that contains all values for tag `hostname` if you specify a query like this in the templating variable *Query* setting.
If you have a variable with key names you can use this variable in a group by clause. This will allow you to change group by using the variable dropdown at the top
SELECT mean("value") FROM "logins" WHERE "hostname" =~ /^$host$/ AND $timeFilter GROUP BY time($__interval), "hostname"
```
`[[varname]]` Example:
```sql
SELECT mean("value") FROM "logins" WHERE "hostname" =~ /^[[host]]$/ AND $timeFilter GROUP BY time($__interval), "hostname"
```
Why two ways? The first syntax is easier to read and write but does not allow you to use a variable in the middle of a word. When the *Multi-value* or *Include all value*
options are enabled, Grafana converts the labels from plain text to a regex compatible string. Which means you have to use `=~` instead of `=`.
InfluxDB supports the special `Ad hoc filters` variable type. This variable allows you to specify any number of key/value filters on the fly. These filters will automatically
