From hourly data to daily data using SQL GROUP BY - sql

Question

I have a table like this:
fld_id fld_DateTime fld_Index
2017-07-01 00:00:00.000 5
2017-07-01 01:00:00.000 10
2017-07-01 02:00:00.000 15
2017-07-01 03:00:00.000 40
...........
...........
2017-07-01 23:00:00.000 70
2017-07-02 00:00:00.000 110
2017-07-02 01:00:00.000 140
2017-07-02 02:00:00.000 190
...............
...............
2017-07-02 23:00:00.000 190
What I am trying to do is to group them and count sum of fld_index per day like so:
fld_id fld_DateTime SUM
2017-07-01 190
2017-07-02 400
Here's what I've tried:
SELECT fld_dateTime, SUM(fld_Index) AS Sum
FROM tbl_data
WHERE
AND fld_ConsDateTime BETWEEN '2017-07-01' AND '2017-08-02'
GROUP BY fld_dateTime
It calculates the sum but still in hourly format. How to achieve the daily format like above example?
UPDATE Monthly Part Output
2017 8 30630800.0000
2017 7 589076201.1800

Answer 1

Simply cast as DATE
SELECT CAST(fld_dateTime AS DATE) AS fld_Date, SUM(fld_Index) AS Sum
FROM tbl_data
WHERE
fld_ConsDateTime BETWEEN '2017-07-01' AND '2017-08-02'
GROUP BY CAST(fld_dateTime AS DATE);
EDIT:
What about month? Is it the same logic?
It depends on your RDBMS, but in SQL Server you could use:
SELECT YEAR(fld_dateTime), MONTH(fld_dateTime), SUM(fld_Index) AS Sum
FROM tbl_data
GROUP BY YEAR(fld_dateTime), MONTH(fld_dateTime);
It is important to add year part to avoid grouping records from different years.

Answer 2

You need to extract the date. In SQL Server, you would do:
SELECT CAST(fld_dateTime as DATE) as fld_date, SUM(fld_Index) AS Sum
FROM tbl_data
WHERE fld_ConsDateTime >= '2017-07-01' AND
fld_ConsDateTime < '2017-08-03'
GROUP BY CAST(fld_dateTime as DATE)
ORDER BY fld_date
In MySQL, the above would work, but I would do:
SELECT DATE(fld_dateTime) as fld_date, SUM(fld_Index) AS Sum
FROM tbl_data
WHERE fld_ConsDateTime >= '2017-07-01' AND
fld_ConsDateTime < '2017-08-03'
GROUP BY DATE(fld_dateTime)
ORDER BY fld_date;
In both cases, you should change the WHERE clause. Your version would keep flights where the date/time is exactly midnight on 2017-08-02. Using >= and < is more accurate -- taking all date/times on one day but not the next.