More efficient way of grouping rows by hour (using a timestamp) - sql-server-2012

Question

I'm trying to show a log of daily transactions that take place. My current method is embarrassingly inefficient and I'm sure there is a much better solution. Here is my current query:
select ReaderMACAddress,
count(typeid) as 'Total Transactions',
SUM(CASE WHEN CAST("Timestamp" as TIME) between '05:00:00' and '11:59:59' THEN 1 ELSE 0 END) as 'Morning(5am-12pm)',
SUM(CASE WHEN CAST("Timestamp" as TIME) between '12:00:00' and '17:59:59' THEN 1 ELSE 0 END) as 'AfternoonActivity(12pm-6pm)',
SUM(CASE WHEN CAST("Timestamp" as TIME) between '18:00:00' and '23:59:59' THEN 1 ELSE 0 END) as 'EveningActivity(6pm-12am)',
SUM(CASE WHEN CAST("Timestamp" as TIME) between '00:00:00' and '04:59:59' THEN 1 ELSE 0 END) as 'OtherActivity(12am-5am)'
from Transactions
where ReaderMACAddress = '0014f54033f5'
Group by ReaderMACAddress;
which returns the results:
ReaderMACAddress Total Transactions Morning(5am-12pm) AfternoonActivity(12pm-6pm) EveningActivity(6pm-12am) OtherActivity(12am-5am)
0014f54033f5 932 269 431 232 0
(sorry for any alignment issues here)
At the moment I only want to look at a single Reader that I specify (through the where clause). Ideally, it would be easier to read if the time sections were in a single column and the results, i.e. a count function were in a second column yielding results such as:
Total Transactions 932
Morning(5am-12pm) 269
AfternoonActivity(12pm-6pm) 431
EveningActivity(6pm-12am) 232
OtherActivity(12am-5am) 0
Thanks for any help :)

Answer 1

I would first consider a computed column, but I believe from a previous post you don't have the ability to change the schema. So how about a view?
CREATE VIEW dbo.GroupedReaderView
AS
SELECT ReaderMACAddress,
Slot = CASE WHEN t >= '05:00' AND t < '12:00' THEN 1
WHEN t >= '12:00' AND t < '18:00' THEN 2
WHEN t >= '18:00' THEN 3 ELSE 4 END
FROM
(
SELECT ReaderMACAddress, t = CONVERT(TIME, [Timestamp])
FROM dbo.Transactions
) AS x;
Now your per-MAC address query is much, much simpler:
SELECT Slot, COUNT(*)
FROM dbo.GroupedReaderView
WHERE ReaderMACAddress = '00...'
GROUP BY Slot;
This will provide a result like:
1 269
2 431
3 232
4 0
You can also add WITH ROLLUP which will provide a grand total with the Slot column being NULL:
SELECT Slot, COUNT(*)
FROM dbo.GroupedReaderView
WHERE ReaderMACAddress = '00...'
GROUP BY Slot
WITH ROLLUP;
Should yield:
1 269
2 431
3 232
4 0
NULL 932
And you can pivot that if you need to, add labels per slot, etc. in your presentation tier.
You could also do it this way, it just makes the view a lot more verbose and pulls a lot of extra data when you query it directly; it's also slightly less efficient to group by strings.
CREATE VIEW dbo.GroupedReaderView
AS
SELECT ReaderMACAddress,
Slot = CASE WHEN t >= '05:00' AND t < '12:00' THEN
'Morning(5am-12pm)'
WHEN t >= '12:00' AND t < '18:00' THEN
'Afternoon(12pm-6pm)'
WHEN t >= '18:00' THEN
'Evening(6pm-12am)'
ELSE
'Other(12am-5am)'
END
FROM
(
SELECT ReaderMACAddress, t = CONVERT(TIME, [Timestamp])
FROM dbo.Transactions
) AS x;
These aren't necessarily more efficient than what you've got, but they're less repetitive and easier on the eyes. :-)
Also if you don't want to (or can't) create a view, you can just put that into a subquery, e.g.
SELECT Slot, COUNT(*)
FROM
(
SELECT ReaderMACAddress,
Slot = CASE WHEN t >= '05:00' AND t < '12:00' THEN
'Morning(5am-12pm)'
WHEN t >= '12:00' AND t < '18:00' THEN
'Afternoon(12pm-6pm)'
WHEN t >= '18:00' THEN
'Evening(6pm-12am)'
ELSE
'Other(12am-5am)'
END
FROM
(
SELECT ReaderMACAddress, t = CONVERT(TIME, [Timestamp])
FROM dbo.Transactions
) AS x
) AS y
WHERE ReaderMACAddress = '00...'
GROUP BY Slot
WITH ROLLUP;
Just an alternative that still lets you use BETWEEN and may be even a little less verbose:
SELECT Slot, COUNT(*)
FROM
(
SELECT ReaderMACAddress,
Slot = CASE WHEN h BETWEEN 5 AND 11 THEN 'Morning(5am-12pm)'
WHEN h BETWEEN 12 AND 17 THEN 'Afternoon(12pm-6pm)'
WHEN h >= 18 THEN 'Evening(6pm-12am)'
ELSE 'Other(12am-5am)'
END
FROM
(
SELECT ReaderMACAddress, h = DATEPART(HOUR, [Timestamp])
FROM dbo.Transactions
) AS x
) AS y
WHERE ReaderMACAddress = '00...'
GROUP BY Slot
WITH ROLLUP;
UPDATE
To always include each slot even if there are no results for that slot:
;WITH slots(s, label, h1, h2) AS
(
SELECT 1, 'Morning(5am-12pm)' , 5, 11
UNION ALL SELECT 2, 'Afternoon(12pm-6pm)' , 12, 17
UNION ALL SELECT 3, 'Evening(6pm-12am)' , 18, 23
UNION ALL SELECT 4, 'Other(12am-5am)' , 0, 4
)
SELECT s.label, c = COALESCE(COUNT(y.ReaderMACAddress), 0)
FROM slots AS s
LEFT OUTER JOIN
(
SELECT ReaderMACAddress, h = DATEPART(HOUR, [Timestamp])
FROM dbo.Transactions
WHERE ReaderMACAddress = '00...'
) AS y
ON y.h BETWEEN s.h1 AND s.h2
GROUP BY s.label
WITH ROLLUP;
The key in all of these cases is to simplify and not repeat yourself. Even if SQL Server only performs it once, why convert to time 4+ times?