grafana/docs/sources/variables/add-query-variable.md

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# Add a query variable

Query variables allow you to write a data source query that can return a list of metric names, tag values, or keys. For example, a query variable might return a list of server names, sensor IDs, or data centers. The variable values change as they dynamically fetch options with a data source query.

Query expressions can contain references to other variables and in effect create linked variables. Grafana detects this and automatically refreshes a variable when one of its linked variables change.

## Query expressions

Query expressions are different for each data source. For more information, refer to the documentation for your [data source]({{< relref "../features/datasources/_index.md" >}}).

## Enter General options

1. Navigate to the dashboard you want to make a variable for and then click the **Dashboard settings** (gear) icon at the top of the page.
1. On the Variables tab, click **New**.
1. Enter a **Name** for your variable.
1. In the **Type** list, select **Query**.
1. (optional) In **Label**, enter the display name of the variable dropdown. If you don't enter a display name, then the dropdown label will be the variable name.
1. Choose a **Hide** option:
   - **No selection (blank) -** The variable dropdown displays the variable **Name** or **Label** value. This is the default.
   - **Label -** The variable dropdown only displays the selected variable value and a down arrow.
   - **Variable -** No variable dropdown is displayed on the dashboard.

## Enter Query Options

1. In the **Data source** list, select the target data source for the query. For more information about data sources, refer to [Add a data source]({{< relref "../features/datasources/add-a-data-source.md" >}}).
1. In the **Refresh** list, select when the variable should update options.
   - **Never -** Variables queries are cached and values are not updated. This is fine if the values never change, but problematic if they are dynamic and change a lot.
   - **On Dashboard Load -** Queries the data source every time the dashboard loads. This slows down dashboard loading, because the variable query needs to be completed before dashboard can be initialized. 
   - **On Time Range Change -** Queries the data source when the dashboard time range changes. Only use this option if your variable options query contains a time range filter or is dependent on the dashboard time range.
1. In the **Query** field, enter a query. 
   - The query field varies according to your data source. Some data sources have custom query editors.
   - If you need more room in a single input field query editor, then hover your cursor over the lines in the lower right corner of the field and drag downward to expand.
2. (optional) In the **Regex** field, type a regex expression to filter or capture specific parts of the names return by your data source query. To see examples, refer to [Filter variables with regex]({{< relref "filter-variables-with-regex.md" >}}).
3. In the **Sort** list, select the sort order for values to be displayed in the dropdown list. The default option, **Disabled**, means that the order of options returned by your data source query will be used.

## Enter Selection Options

All selection options are optional, and they are off by default.

### Multi-value

If you turn this on, then the variable dropdown list allows users to select multiple options at the same time. For more information, refer to [Formatting multi-value variables]({{< relref "formatting-multi-value-variables.md" >}}).

### Include All option

Grafana adds an `All` option to the variable dropdown list. If a user selects this option, then all variable options are selected.

### Custom all value

This option is only visible if the **Include All option** is selected.

Enter regex, globs, or lucene syntax in the **Custom all value** field to define the value of the `All` option.

By default the `All` value includes all options in combined expression. This can become very long and can have performance problems. Sometimes it can be better to specify a custom all value, like a wildcard regex. 

In order to have custom regex, globs, or lucene syntax in the **Custom all value** option, it is never escaped so you will have to think about what is a valid value for your data source.

## Enter Value groups/tags (experimental feature)

If you have many options in the dropdown for a multi-value variable, then you can use this feature to group the values into selectable tags.

{{< docs-imagebox img="/img/docs/v50/variable_dropdown_tags.png" max-width="300px" >}}

This feature is off by default. Click **Enabled** to turn on the feature.

### Tags query

Enter a data source query that should return a list of tags. The tags query returns a list of tags that each represent a group, and the tag values query returns a list of group members. 

For example, the tags query could be a list of regions (Europe, Asia, Americas), and then if the user selects the Europe tag, then the tag values query would return a list of countries -- Sweden, Germany, France, and so on.

If you have a variable with a lot of values (say all the countries in the world), then this allows you to easily select a group of them. If the user selects the tag Europe, all the countries in Europe would be selected.

In this [example dashboard](https://play.grafana.org/d/ZUPhFVGGk/graphite-with-experimental-tags?orgId=1), the server variable has tags enabled. 

### Tag values query

Enter a data source query that should return a list of values for a specified tag key. Use `$tag` in the query to refer the currently selected tag.

The `$tag` variable will have the value of the tag that the user chooses. 

For example, if you have a Graphite query for tags, `regions.*`, that returns a list of regions. The the values query could be `regions.$tag.*`, which if the user chooses Europe would be interpolated to `regions.Europe.*`.

## Final steps

1. In **Preview of values**, Grafana displays a list of the current variable values. Review them to ensure they match what you expect.
1. Click **Add** to add the variable to the dashboard.