specify grafana version for last fill mode

docs/sources/features/datasources/mssql.md

@@ -83,7 +83,7 @@ Macro example | Description
 *$__timeGroup(dateColumn,'5m'[, fillvalue])* | Will be replaced by an expression usable in GROUP BY clause. Providing a *fillValue* of *NULL* or *floating value* will automatically fill empty series in timerange with that value. <br/>For example, *CAST(ROUND(DATEDIFF(second, '1970-01-01', time_column)/300.0, 0) as bigint)\*300*.
 *$__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', last)* | Same as above but the last seen value in that series will be used as fill value if no value has been seen yet NULL will be used.
+*$__timeGroup(dateColumn,'5m', last)* | Same as above but the last seen value in that series will be used as fill value if no value has been seen yet NULL will be used (only available in Grafana 5.3+).
 *$__timeGroupAlias(dateColumn,'5m')* | Will be replaced identical to $__timeGroup but with an added column alias (only available in Grafana 5.3+).
 *$__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*

docs/sources/features/datasources/mysql.md

@@ -66,7 +66,7 @@ Macro example | Description
 *$__timeGroup(dateColumn,'5m')* | Will be replaced by an expression usable in GROUP BY clause. For example, *cast(cast(UNIX_TIMESTAMP(dateColumn)/(300) as signed)*300 as signed),*
 *$__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', last)* | Same as above but the last seen value in that series will be used as fill value if no value has been seen yet NULL will be used.
+*$__timeGroup(dateColumn,'5m', last)* | Same as above but the last seen value in that series will be used as fill value if no value has been seen yet NULL will be used (only available in Grafana 5.3+).
 *$__timeGroupAlias(dateColumn,'5m')* | Will be replaced identical to $__timeGroup but with an added column alias (only available in Grafana 5.3+).
 *$__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*

docs/sources/features/datasources/postgres.md

@@ -64,6 +64,7 @@ Macro example | Description
 *$__timeGroup(dateColumn,'5m', 0)* | Same as above but with a fill parameter so missing points in that series will be added by grafana and 0 will be used as value.
 *$__timeGroup(dateColumn,'5m', NULL)* | Same as above but NULL will be used as value for missing points.
 *$__timeGroup(dateColumn,'5m', last)* | Same as above but the last seen value in that series will be used as fill value if no value has been seen yet NULL will be used.
+*$__timeGroup(dateColumn,'5m', last)* | Same as above but the last seen 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+).
 *$__timeGroupAlias(dateColumn,'5m')* | Will be replaced identical to $__timeGroup but with an added column alias (only available in Grafana 5.3+).
 *$__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*