How to difference between group by and group by all in SQL

hI tOANHOI
Please check this...

http://www.w3schools.com/sql/sql_groupby.asp

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The "Group By All" returns all groups even if some groups have no rows. But "Group By" returns only those groups which has rows.

You may go through below link for more details:

http://msdn.microsoft.com/en-us/library/ms175028(v=sql.90).aspx