MSSQL server SQL query how to utilize "group by" - sql-server-2005

Question

Table Data
My_table_data.
testdate plant value
2020-05-14 02:00:00.000 1 68
2020-05-14 01:00:00.000 3 115
2020-05-14 02:00:00.000 2 107
2020-05-14 03:00:00.000 2 102
2020-05-14 05:00:00.000 2 104
2020-05-14 06:00:00.000 2 111
2020-05-14 08:00:00.000 1 74
2020-05-14 08:00:00.000 2 114
2020-05-14 09:00:00.000 1 70
2020-05-14 09:00:00.000 2 114
2020-05-14 03:00:00.000 3 106
2020-05-14 03:00:00.000 3 102
2020-05-15 02:00:00.000 2 108
2020-05-14 05:00:00.000 1 74
2020-05-14 04:00:00.000 3 96
2020-05-14 04:00:00.000 3 97
2020-05-14 06:00:00.000 1 80
2020-05-14 03:00:00.000 1 77
2020-05-14 06:00:00.000 3 102
I am novice at complex SQL query phrase. How to achieve the result like below.
Conditions
1. Latest data on timestamp(Hour)
2. single row for each plant.
WITH data AS(
SELECT testdate, plant, value, (DATEPART(HOUR,testdate))AS dH FROM My_table_data
WHERE testdate >= (SELECT CONVERT(DATETIME, CONVERT(DATE, GETDATE()), 120))
)
SELECT data.testdate, data.plant, data.value from data
WHERE data.dH= (SELECT MAX(data.dH) FROM data)
GROUP BY data.plant
ORDER BY data.plant DESC;
It gives error!!
testdate Plant value
2020-05-14 09:00:00.000 1 70
2020-05-14 09:00:00.000 2 114
2020-05-14 06:00:00.000 3 102

Answer 1

I think this should be as simple as
with maxData
AS
(
SELECT MAX(testDate) as testDate, plantId
FROM My_table_data
GROUP BY plantId
)
select
t.testDate,
t.plantId,
t.value
from My_table_data t
INNER JOIN maxData m
on t.testDate = m.testDate
and t.plantId = m.plantId
order by plantId
WHat this does is uses a CTE to find the max date for every plantId and then joins that info back to the original table to find the value corresponding to that plantId and date.