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title = "Add a query variable"
type = "docs"
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weight = 500
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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.
1. (optional) In the **Regex** field, type a regex expression to filter or capture specific parts of the names returned by your data source query. To see examples, refer to [Filter variables with regex]({{< relref "filter-variables-with-regex.md" >}}).
1. 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.
1. (optional) Enter [Selection Options]({{< relref "variable-selection-options.md" >}}).
1. (optional) Enter [Value groups/tags]({{< relref "variable-value-tags.md" >}}).
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.