Group by date only on a Datetime column

Having a table with a column like: mydate DATETIME ...

I have a query such as:

SELECT SUM(foo), mydate FROM a_table GROUP BY a_table.mydate;

This will group by the full datetime, including hours and minutes. I wish to make the group by, only by the date YYYY/MM/DD not by the YYYY/MM/DD/HH/mm.

How to do this?

Cast the datetime to a date, then GROUP BY using this syntax:

SELECT SUM(foo), DATE(mydate) FROM a_table GROUP BY DATE(a_table.mydate);

Or you can GROUP BY the alias as @orlandu63 suggested:

SELECT SUM(foo), DATE(mydate) DateOnly FROM a_table GROUP BY DateOnly;

Though I don't think it'll make any difference to performance, it is a little clearer.

I found that I needed to group by the month and year so neither of the above worked for me. Instead I used date_format

SELECT date
FROM blog 
GROUP BY DATE_FORMAT(date, "%m-%y")
ORDER BY YEAR(date) DESC, MONTH(date) DESC 

Or:

SELECT SUM(foo), DATE(mydate) mydate FROM a_table GROUP BY mydate;

More efficient (I think.) Because you don't have to cast mydate twice per row.

SELECT SUM(No), HOUR(dateofissue) 
FROM tablename 
WHERE dateofissue>='2011-07-30' 
GROUP BY HOUR(dateofissue)

It will give the hour by sum from a particular day!

this worked for me

select 
  CONVERT(date, CONVERT(VARCHAR(10),sd.Date,112)) as Date, 
  sd.CodId as CodId,
  p.Description ,
  sum(sd.Quantity)as Quantity,
  sum(sd.TotalQuantityXPriceWithIva) as TotalWithIva 
from 
  SaleDetails sd 
  join Sales s on sd.SaleId = s.SaleId 
  join Products p on sd.ProductId = p.ProductId 
Where 
  (
    sd.Date >=' 1/1/2021 00:00:00' 
    and sd.Date <= '26/10/2021 23:59:59' 
    and p.BarCode = '7790628000034'
    and ((s.VoucherTypeId >= 16 and s.VoucherTypeId <= 18) 
      or s.VoucherTypeId = 32  )) 
group by 
  CONVERT(VARCHAR(10),sd.Date,112), 
  sd.CodId , 
  p.Description 
order by CONVERT(VARCHAR(10),sd.Date,112) desc