Use of Rollup, Grouping, Grouping_ID and Cube in Group By

ROLLUP = Generates the simple GROUP BY aggregate rows
  , plus subtotal or super-aggregate rows
  , and also a grand total row.
GROUPING = Indicates whether a specified column expression in a GROUP BY list is aggregated or not.
GROUPING_ID = Is a function that computes the level of grouping.
CUBE = Generates simple GROUP BY aggregate rows, the ROLLUP super-aggregate rows, and cross-tabulation rows.
Sample Data
DECLARE @Sales TABLE (Year INT, Quarter VARCHAR(50), SalesPerson VARCHAR(50), Amount FLOAT)

INSERT INTO @Sales values
      (1998, 'Q1', 'SalePerson1', 123)
    , (1998, 'Q2', 'SalePerson2', 234)
    , (1998, 'Q3', 'SalePerson4', 345)
    , (1998, 'Q4', 'SalePerson3', 556)
    , (1999, 'Q1', 'SalePerson1', 623)
    , (1999, 'Q2', 'SalePerson2', 734)
    , (1999, 'Q3', 'SalePerson3', 845)
    , (1999, 'Q4', 'SalePerson4', 956)

Example 1 : (Single field in grouping)

SELECT
     [Year]
    , AVG(Amount) as Average
    , GROUPING([Year]) as [YearRollUp?]
FROM 
    @Sales
GROUP BY
    [Year] WITH ROLLUP

Output :

Year        Average                YearRollUp?
----------- ---------------------- -----------
1998        314.5                  0
1999        789.5                  0
NULL        552                    1

Example 2 : (Multipal field in grouping)

SELECT
    [Year]
    , Quarter
    , AVG(Amount) as Average
    , GROUPING( [Year] ) as [YearRollUp?]
FROM 
    @Sales
GROUP BY
    GROUPING SETS (( [Year], Quarter), ( [Year] ), ())

Output : 

Year        Quarter Average                YearRollUp?
----------- ------- ---------------------- -----------
1998        Q1      123                    0
1998        Q2      234                    0
1998        Q3      345                    0
1998        Q4      556                    0
1998        NULL    314.5                  0
1999        Q1      623                    0
1999        Q2      734                    0
1999        Q3      845                    0
1999        Q4      956                    0
1999        NULL    789.5                  0
NULL        NULL    552                    1

Example 3 :( Example of Grouping_ID )

SELECT
    [Year]
    , Quarter
    , AVG(Amount) as Average
    , GROUPING_ID( [Year], Quarter) as [x]
FROM 
    @Sales
GROUP BY
    GROUPING SETS (( [Year], Quarter), ( [Year] ), ( [Quarter] ), ())

Output :

Year        Quarter Average                x
----------- ------- ---------------------- -----------
1998        Q1      123                    0
1999        Q1      623                    0
NULL        Q1      373                    2
1998        Q2      234                    0
1999        Q2      734                    0
NULL        Q2      484                    2
1998        Q3      345                    0
1999        Q3      845                    0
NULL        Q3      595                    2
1998        Q4      556                    0
1999        Q4      956                    0
NULL        Q4      756                    2
NULL        NULL    552                    3
1998        NULL    314.5                  1
1999        NULL    789.5                  1

Example 4:(Example of Cube)

SELECT
     [Year]
    , [Quarter]
    , AVG(Amount) as Average
    , GROUPING_ID( [Year], [Quarter]) as [x]
FROM 
    @Sales
GROUP BY
    CUBE( [Year], [Quarter])

Output :

Year        Quarter Average                x
----------- ------- ---------------------- -----------
1998        Q1      123                    0
1999        Q1      623                    0
NULL        Q1      373                    2
1998        Q2      234                    0
1999        Q2      734                    0
NULL        Q2      484                    2
1998        Q3      345                    0
1999        Q3      845                    0
NULL        Q3      595                    2
1998        Q4      556                    0
1999        Q4      956                    0
NULL        Q4      756                    2
NULL        NULL    552                    3
1998        NULL    314.5                  1
1999        NULL    789.5                  1

Multipal Field Group By IN LINQ

var objOrderList = from OrderList in
        (from OrderDetail in objOrderDetail
      join Item in objItem on OrderDetail.ItemId equals Item.ItemId
      join ItemGroup in objItemGroup on Item.GroupId equals ItemGroup.GroupId
      select new
      {
       GroupName = ItemGroup.GroupName,
       ItemName = Item.ItemName,
       Rate = Item.Rate,
       Qty = OrderDetail.Qty
      }
      )
       group OrderList by new
       {
        OrderList.GroupName,
        OrderList.ItemName
       } into OrderList
       select new
       {
        GroupName = OrderList.Key.GroupName,
        ItemName = OrderList.Key.ItemName,
        OrderTotal = OrderList.Sum(OL => OL.Qty * OL.Rate)
       };

Left Outer Join and Group By In LINQ

List Table1 = new List();
List Table2 = new List();

var objList = from ListData in
                  (from a in Table1
                   join b in Table2 on a.Id equals b.Id into t2
                   from t2Data in t2.DefaultIfEmpty()
                   select new
                   {
                       Product = a.Product,
                       Title = t2Data.Title,
                       Amount = a.Amount
                   }
                )
              group ListData by new
              {
                  ListData.Product,
                  ListData.Title
              } into GroupData
              select new
              {
                  Product = GroupData.Key.Product,
                  Title = GroupData.Key.Title,
                  Amount = GroupData.Sum(OL => OL.Amount)
              };