MySQL/SQL: Group by date only on a Datetime column

Question

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.myd         


        

Answer 1

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.