SQL query to group by day

I want to list all sales, and group the sum by day.

Sales (saleID INT, amount INT, created DATETIME)

NOTE: I am using SQL Server 2005.

if you're using SQL Server,

dateadd(DAY,0, datediff(day,0, created)) will return the day created

for example, if the sale created on '2009-11-02 06:12:55.000', dateadd(DAY,0, datediff(day,0, created)) return '2009-11-02 00:00:00.000'

select sum(amount) as total, dateadd(DAY,0, datediff(day,0, created)) as created
from sales
group by dateadd(DAY,0, datediff(day,0, created))

For SQL Server:

GROUP BY datepart(year,datefield), 
    datepart(month,datefield), 
    datepart(day,datefield)

or faster (from Q8-Coder):

GROUP BY dateadd(DAY,0, datediff(day,0, created))

For MySQL:

GROUP BY year(datefield), month(datefield), day(datefield)

or better (from Jon Bright):

GROUP BY date(datefield)

For Oracle:

GROUP BY to_char(datefield, 'yyyy-mm-dd')

or faster (from IronGoofy):

GROUP BY trunc(created);

For Informix (by Jonathan Leffler):

GROUP BY date_column
GROUP BY EXTEND(datetime_column, YEAR TO DAY)

If you're using MySQL:

SELECT
    DATE(created) AS saledate,
    SUM(amount)
FROM
    Sales
GROUP BY
    saledate

If you're using MS SQL 2008:

SELECT
    CAST(created AS date) AS saledate,
    SUM(amount)
FROM
    Sales
GROUP BY
    CAST(created AS date)

actually this depends on what DBMS you are using but in regular SQL convert(varchar,DateColumn,101) will change the DATETIME format to date (one day)

so:

SELECT 
    sum(amount) 
FROM 
    sales 
GROUP BY 
    convert(varchar,created,101)

the magix number 101 is what date format it is converted to

If you're using SQL Server, you could add three calculated fields to your table:

Sales (saleID INT, amount INT, created DATETIME)

ALTER TABLE dbo.Sales
  ADD SaleYear AS YEAR(Created) PERSISTED
ALTER TABLE dbo.Sales
  ADD SaleMonth AS MONTH(Created) PERSISTED
ALTER TABLE dbo.Sales
  ADD SaleDay AS DAY(Created) PERSISTED

and now you could easily group by, order by etc. by day, month or year of the sale:

SELECT SaleDay, SUM(Amount)
FROM dbo.Sales
GROUP BY SaleDay

Those calculated fields will always be kept up to date (when your "Created" date changes), they're part of your table, they can be used just like regular fields, and can even be indexed (if they're "PERSISTED") - great feature that's totally underused, IMHO.

Marc