> Starting from Grafana v5.1 you can name the time column *time* in addition to earlier supported *time_sec*. Usage of *time_sec* will eventually be deprecated.
*Max open* | The maximum number of open connections to the database, default `unlimited` (Grafana v5.4+).
*Max idle* | The maximum number of connections in the idle connection pool, default `2` (Grafana v5.4+).
*Max lifetime* | The maximum amount of time in seconds a connection may be reused, default `14400`/4 hours. This should always be lower than configured [wait_timeout](https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_wait_timeout) in MySQL (Grafana v5.4+).
A lower limit for the [$__interval](/reference/templating/#the-interval-variable) and [$__interval_ms](/reference/templating/#the-interval-ms-variable) variables.
Recommended to be set to write frequency, for example `1m` if your data is written every minute.
This option can also be overridden/configured in a dashboard panel under data source options. It's important to note that this value **needs** to be formatted as a
number followed by a valid time identifier, e.g. `1m` (1 minute) or `30s` (30 seconds). The following time identifiers are supported:
*$__time(dateColumn)* | Will be replaced by an expression to convert to a UNIX timestamp and rename the column to `time_sec`. For example, *UNIX_TIMESTAMP(dateColumn) as time_sec*
*$__timeEpoch(dateColumn)* | Will be replaced by an expression to convert to a UNIX timestamp and rename the column to `time_sec`. For example, *UNIX_TIMESTAMP(dateColumn) as time_sec*
*$__timeFilter(dateColumn)* | Will be replaced by a time range filter using the specified column name. For example, *dateColumn BETWEEN '2017-04-21T05:01:17Z' AND '2017-04-21T05:06:17Z'*
*$__timeFrom()* | Will be replaced by the start of the currently active time selection. For example, *'2017-04-21T05:01:17Z'*
*$__timeTo()* | Will be replaced by the end of the currently active time selection. For example, *'2017-04-21T05:06:17Z'*
*$__timeGroup(dateColumn,'5m')* | Will be replaced by an expression usable in GROUP BY clause. For example, *cast(cast(UNIX_TIMESTAMP(dateColumn)/(300) as signed)*300 as signed),*
*$__timeGroup(dateColumn,'5m', 0)* | Same as above but with a fill parameter so missing points in that series will be added by grafana and 0 will be used as value.
*$__timeGroup(dateColumn,'5m', NULL)* | Same as above but NULL will be used as value for missing points.
*$__timeGroup(dateColumn,'5m', previous)* | Same as above but the previous value in that series will be used as fill value if no value has been seen yet NULL will be used (only available in Grafana 5.3+).
*$__unixEpochFilter(dateColumn)* | Will be replaced by a time range filter using the specified column name with times represented as unix timestamp. For example, *dateColumn > 1494410783 AND dateColumn < 1494497183*
*$__unixEpochFrom()* | Will be replaced by the start of the currently active time selection as unix timestamp. For example, *1494410783*
*$__unixEpochTo()* | Will be replaced by the end of the currently active time selection as unix timestamp. For example, *1494497183*
We plan to add many more macros. If you have suggestions for what macros you would like to see, please [open an issue](https://github.com/grafana/grafana) in our GitHub repo.
The query editor has a link named `Generated SQL` that show up after a query as been executed, while in panel edit mode. Click on it and it will expand and show the raw interpolated SQL string that was executed.
If the `Format as` query option is set to `Table` then you can basically do any type of SQL query. The table panel will automatically show the results of whatever columns & rows your query returns.
If you set `Format as` to `Time series`, for use in Graph panel for example, then the query must return a column named `time` that returns either a sql datetime or any numeric datatype representing unix epoch.
Any column except `time` and `metric` is treated as a value column.
You may return a column named `metric` that is used as metric name for the value column.
If you return multiple value columns and a column named `metric` then this column is used as prefix for the series name (only available in Grafana 5.3+).
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 MySQL 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 my_host
```
A query can returns 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 my_host.hostname, my_other_host.hostname2 FROM my_host JOIN my_other_host ON my_host.city = my_other_host.city
To use time range dependent macros like `$__timeFilter(column)` in your query the refresh mode of the template variable needs to be set to *On Time Range Change*.
```sql
SELECT event_name FROM event_log WHERE $__timeFilter(time_column)
Another option is a query that can create a key/value variable. The query should return two columns that are named `__text` and `__value`. The `__text` column value should be unique (if it is not unique then the first value is used). The options in the dropdown will have a text and value that allows you to have a friendly name as text and an id as the value. An example query with `hostname` as the text and `id` as the value:
```sql
SELECT hostname AS __text, id AS __value FROM my_host
You can also create nested variables. For example if you had another variable named `region`. Then you could have
the hosts variable only show hosts from the current selected region with a query like this (if `region` is a multi-value variable then use the `IN` comparison operator rather than `=` to match against multiple values):
```sql
SELECT hostname FROM my_host WHERE region IN($region)
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 4.7.0, 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.
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'`. Do disable quoting, use the csv formatting option for variables:
[Annotations]({{< relref "reference/annotations.md" >}}) allow you to overlay rich event information on top of graphs. You add annotation queries via the Dashboard menu / Annotations view.
It's now possible to configure datasources using config files with Grafana's provisioning system. You can read more about how it works and all the settings you can set for datasources on the [provisioning docs page](/administration/provisioning/#datasources)