For an introduction to templating and template variables, refer to the [Templating](ref:variables) and [Add and manage variables](ref:add-template-variables) documentation.
If you add a template variable of the type `Query`, you can write a MS SQL query that can
return things like measurement names, key names or key values that are shown as a dropdown select box.
For example, you can have a variable that contains all values for the `hostname` column in a table if you specify a query like this in the templating variable **Query** setting.
```sql
SELECT hostname FROM host
```
A query can return multiple columns and Grafana will automatically create a list from them. For example, the query below will return a list with values from `hostname` and `hostname2`.
```sql
SELECT [host].[hostname], [other_host].[hostname2] FROM host JOIN other_host ON [host].[city] = [other_host].[city]
```
Another option is a query that can create a key/value variable. The query should return two columns that are named `__text` and `__value`. The `__text` column value should be unique (if it is not unique then the first value is used). The options in the dropdown will have a text and value that allow you to have a friendly name as text and an id as the value. An example query with `hostname` as the text and `id` as the value:
```sql
SELECT hostname __text, id __value FROM host
```
You can also create nested variables. For example, if you had another variable named `region`. Then you could have
the hosts variable only show hosts from the current selected region with a query like this (if `region` is a multi-value variable, then use the `IN` comparison operator rather than `=` to match against multiple values):
```sql
SELECT hostname FROM host WHERE region IN ($region)
```
## Using variables in queries
> From Grafana 4.3.0 to 4.6.0, template variables are always quoted automatically so if it is a string value do not wrap them in quotes in where clauses.
>
> From Grafana 5.0.0, template variable values are only quoted when the template variable is a `multi-value`.
If the variable is a multi-value variable then use the `IN` comparison operator rather than `=` to match against multiple values.
There are two syntaxes:
`$<varname>` Example with a template variable named `hostname`:
```sql
SELECT
atimestamp time,
aint value
FROM table
WHERE $__timeFilter(atimestamp) and hostname in($hostname)
ORDER BY atimestamp
```
`[[varname]]` Example with a template variable named `hostname`:
```sql
SELECT
atimestamp as time,
aint as value
FROM table
WHERE $__timeFilter(atimestamp) and hostname in([[hostname]])
Grafana automatically creates a quoted, comma-separated string for multi-value variables. For example: if `server01` and `server02` are selected then it will be formatted as: `'server01', 'server02'`. To disable quoting, use the csv formatting option for variables:
