Group a sub-set of a result set by time interval - sql

Question

I have an audit table where specific actions are being recorded (such as 'access', 'create', 'update' and so on). I am selecting these records so that they can be displayed in a table to the administrative user.
This works fine when I select all the records for a particular entity. However, because I am using the Post-Redirect-Get pattern, the 'access' records are being logged on every page view. In a typical session an end user may hit the same page 6 or 7 times in the same 5 minute window. As a consequence, the administrative user is having to scroll through quite a few redundant access records and this is understandably distracting from the user experience.
To solve this problem, I have written two queries. The first will look for all records that are not access records. The second will look for access records and then groups them into ten minute intervals. I then UNION these two queries and order by the datetime.
-- Select non 'access' records
SELECT
[ORIGIN_ID]
,[ORIGIN_ID_TYPE]
,[REFERENCE_ID]
,[REFERENCE_ID_TYPE]
,[ACTION_TYPE_ID]
,CAST([ORIGINAL_VALUE] AS VARCHAR(8000)) AS ORIGINAL_VALUE
,CAST([CHANGED_VALUE] AS VARCHAR(8000)) AS CHANGED_VALUE
,[CREATED_BY]
,[CREATED_ON]
FROM [HISTORY]
WHERE [ORIGIN_ID] = 500 AND [ORIGIN_ID_TYPE] = 4 AND [ACTION_TYPE_ID] != 1
UNION
-- Select 'access' records and group them into 10 minute intervals by ts
SELECT
[ORIGIN_ID]
,[ORIGIN_ID_TYPE]
,[REFERENCE_ID]
,[REFERENCE_ID_TYPE]
,[ACTION_TYPE_ID]
,CAST([ORIGINAL_VALUE] AS VARCHAR(255)) AS ORIGINAL_VALUE
,CAST([CHANGED_VALUE] AS VARCHAR(255)) AS CHANGED_VALUE
,[CREATED_BY]
,DATEADD(MINUTE, DATEDIFF(MINUTE, 0, [CREATED_ON]) / 10 * 10, 0) AS CREATED_ON
FROM [HISTORY]
WHERE [ACTION_TYPE_ID] = 1 AND [ORIGIN_ID] = 500 AND [ORIGIN_ID_TYPE] = 4
GROUP BY
[ORIGIN_ID]
,[ORIGIN_ID_TYPE]
,[REFERENCE_ID]
,[REFERENCE_ID_TYPE]
,[ACTION_TYPE_ID]
,CAST([ORIGINAL_VALUE] AS VARCHAR(255))
,CAST([CHANGED_VALUE] AS VARCHAR(255))
,[CREATED_BY]
,DATEADD(MINUTE, DATEDIFF(MINUTE, 0, [CREATED_ON]) / 10 * 10, 0)
ORDER BY [CREATED_ON] DESC
SQLFiddle (I had a limited amount of data SQLFiddle would allow me to upload)
I feel like there may be a better way to do this that does not require me to use UNION. In order to do it this way I had to cast my TEXT columns to VARCHAR columns and I feel like there could be a better alternative. Any suggestions as to how this query can be improved?

Answer 1

Eliminate the union by using these two groupings. The second one also becomes the new expression for the combined created_on column. The first can also be used to control sorting and then otherwise discarded. (Don't forget to remove the filter on action_type_id too.):
case when action_type_id <> 1 then 1 else 2 end,
case when action_type_id <> 1
then created_on
else DATEADD(MINUTE, DATEDIFF(MINUTE, 0, [CREATED_ON]) / 10 * 10, 0)
end
This will cause the query to treat the two types of actions as distinct for purposes of aggregation. Since you do want to keep every row with a non-1 action, you don't collapse those into ten-minute blocks at all.
Note that this wouldn't quite work as is if it's possible to have two such rows recorded with the same timestamp. You'd need to group on another ID (or just row_number()) to get around that but I suspect that'll be unnecessary.