All columns in the SELECT clause that do not have an aggregate need to be in the GROUP BY

Good:

SELECT col1, col2, col3, MAX(col4)
...
GROUP BY col1, col2, col3

Also good:

SELECT col1, col2, col3, MAX(col4)
...
GROUP BY col1, col2, col3, col5, col6

No other columns = no GROUP BY needed

SELECT MAX(col4)
...

Won't work:

SELECT col1, col2, col3, MAX(col4)
...
GROUP BY col1, col2

Pointless:

SELECT col1, col2, col3, MAX(col4)
...
GROUP BY col1, col2, col3, MAX(col4)

Having an aggregate (MAX etc) with other columns without a GROUP BY makes no sense because the query becomes ambiguous.

You can use Select AGG() OVER() in TSQL

SELECT *,
SUM(Value) OVER()
FROM Table

There are other options for Over such as Partition By if you want to group:

SELECT *,
SUM(Value) OVER(PARTITION By ParentId)
FROM Table

http://msdn.microsoft.com/en-us/library/ms189461.aspx

Yes you can use an aggregate without GROUP BY:

SELECT SUM(col) FROM tbl;

This will return one row only - the sum of the column "col" for all rows in tbl (excluding nulls).

You must group by columns that do not have aggregate functions on them.

You may avoid a group by clause if all columns selected have aggregate functions applied.

The Columns which are not present in the Aggregate function should come on group by clause:

Select 
Min(col1), 
Avg(col2), 
sum(col3) 
from table

then we do not required group by clause, But if there is some column which are not present in the Aggregate function then you must use group by for that column.

Select 
col1, 
col2, 
sum(col3) 
from  table 
group by col1,col2

then we have to use the group by for the column col1 and col2

You omit columns from the SELECT inside aggregate functions, all other columns should exist in GROUP BY clause seperated by comma.

You can have query with aggregates and no group by, as long as you have ONLY aggregate values in the SELECT statement

Yes, without aggregate functions we can use group by column but it will be a distinct function.

select <column name> from <table name> group by <column name>

Given the table EMP :

select * from EMP

That outputs:

7369    SMITH   CLERK       7902
7499    ALLEN   SALESMAN    7698
7521    WARD    SALESMAN    7698
7566    JONES   MANAGER     7839

Adding a group by

select job from EMP group by job

Outputs:

CLERK
SALESMAN
MANAGER