在 sql 中按日期分组并以日期时间显示

Question

i want to count the data then group by date (and it show in date time). the result of data type must date time not var char. any idea?

table_a

timestamp
2020-11-28 04:00:00
2020-11-28 05:00:00
2020-11-29 01:00:00
2020-11-29 02:00:00
2020-11-29 03:00:00

expected result:

timestamp                 count
2020-11-28 00:00:00       2
2020-11-29 00:00:00       3

if i query this:

select date(timestamp), count(*) as count
from table_a
group by date(timestamp)

the result is:

timestamp     count
2020-11-28     2
2020-11-29     3

Answer 1

You can truncate the time part with DATE(timestamp) and cast back to DATETIME with the function CAST() :

SELECT CAST(DATE(timestamp) AS DATETIME) AS my_datetime, 
       COUNT(*) AS count 
FROM table_a
GROUP BY my_datetime;

See the demo .
Results:

> my_datetime         | count
> :------------------ | ----:
> 2020-11-28 00:00:00 |     2
> 2020-11-29 00:00:00 |     3

Answer 2

Use this code:

CAST(MED_TO_DT AS DATETIME)

You can use CAST date field to datetime.

Answer 3

If you want to group by the date AND time, use this query:

select CONVERT(timestamp, datetime) as timestamp, count(1) as count
from table_a
group by CONVERT(timestamp, datetime)

Otherwise, if you truly want to group by the date ONLY and then display the timestamp as 00:00:00, then use this query:

select CONVERT(CONVERT(timestamp, date), datetime) as timestamp, count(1) as count
from table_a
group by CONVERT(timestamp, date)

Answer 4

MYSQL:

SELECT Concat(Cast(timestamp AS DATE), " 00:00:00") AS timestamps, 
       Count(*)                                     AS count 
FROM   table_a 
GROUP  BY timestamps