What are differences between system.stringbuilder and system.string?

What are differences between system.stringbuilder and system.string?

The main difference is system.string is immutable and system.stringbuilder is a mutable. Append keyword is used in string builder but not in system.string.

Immutable means once we created we cannot modified. Suppose if we want give new value to old value simply it will discarded the old value and it will create new instance in memory to hold the new value.

Difference between Abstract and Interface

Abstract Class:

-Abstract class provides a set of rules to implement next class
-Rules will be provided through abstract methods
-Abstract method does not contain any definition
-While inheriting abstract class all abstract methods must be override
-If a class contains at least one abstract method then it must be declared as an “Abstract Class”
-Abstract classes cannot be instantiated (i.e. we cannot create objects), but a reference can be created
-Reference depends on child class object’s memory
-Abstract classes are also called as “Partial abstract classes”
-Partial abstract class may contain functions with body and functions without body
-If a class contains all functions without body then it is called as “Fully Abstract Class” (Interface)

Interface:

-If a class contains all abstract methods then that class is known as “Interface”
-Interfaces support like multiple inheritance
-In interface all methods r public abstract by default
-Interfaces r implementable
-Interfaces can be instantiated, but a reference cannot be created

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DATE DIFFRENCE in MS SQL

Declare

    @workingDays int,
    @Count int,
@totWekends int,
    @startdate datetime = getdate(),
    @enddate datetime = getdate()+6

set @Count=6+1;

  set @workingDays= (DATEDIFF(dd, @StartDate, @EndDate) + 1) -(DATEDIFF(wk, @StartDate, @EndDate) * 2)
  -(case datepart(dw, @StartDate)+@@datefirst when 8 then 1 else 0 end)
  -(case datepart(dw, @EndDate)+@@datefirst when 7 then 1 when 14 then 1 else 0 end)

set @totWekends=@Count-@workingDays
select  CONVERT(VARCHAR(10),DATEADD(day,@workingDays+@totWekends,getdate()),103) AS LastDate

Pivot table in ms sql

-- Sample data
declare @T table
(
  ID int,
  Title nvarchar(10),
  FieldsXml nvarchar(max)
)
insert into @T values
(1,     'A',       '<Fields><Field Name="X">x1</Field><Field Name="Y">y1</Field></Fields>'),
(2,     'B',       '<Fields><Field Name="Y">y2</Field><Field Name="Z">z2</Field></Fields>'),
(3,     'C',       '<Fields><Field Name="Z">z3</Field></Fields>')

-- Create temp table
select T.ID,
       T.Title,
       TN.X.value('@Name', 'nvarchar(128)') as FieldName,
       TN.X.value('.', 'nvarchar(max)') as FieldValue
into #tmp      
from @T as T    
  cross apply (select cast(FieldsXml as XML)) as TX(X)
  cross apply TX.X.nodes('/Fields/Field') as TN(X)


declare @ColList nvarchar(max)
declare @Sql nvarchar(max)

-- Build column list
select @ColList = stuff((select '], ['+FieldName
                         from #tmp
                         group by FieldName
                         for xml path('')), 1, 2, '')+']'
select * from  #tmp
-- Build query
set @Sql = 'select *
            from (select ID,
                         Title,
                         FieldName,
                         FieldValue
                  from #tmp
                 ) as T
            pivot (min(FieldValue) for FieldName in (' + @ColList + ')) as P'

exec (@Sql)

drop table #tmp

binary tree structure with child count

DECLARE @Data TABLE (
  ID INTEGER PRIMARY KEY
  , ParentID INTEGER
  , Text VARCHAR(32)
  , Price INTEGER
)

INSERT INTO @Data
  SELECT 1, Null, 'Root', NULL
  UNION ALL SELECT 2, 1, 'Flowers', NULL
  UNION ALL SELECT 3, 1, 'Electro', NULL
  UNION ALL SELECT 4, 2, 'Rose', 10
  UNION ALL SELECT 5, 2, 'Violet', 5
  UNION ALL SELECT 6, 4, 'Red Rose', 12
  UNION ALL SELECT 7, 3, 'Television', 100
  UNION ALL SELECT 8, 3, 'Radio', 70
  UNION ALL SELECT 9, 8, 'Webradio', 90

  ;WITH ChildrenCTE AS (
  SELECT  RootID = ID, ID
  FROM    @Data
  UNION ALL
  SELECT  cte.RootID, d.ID
  FROM    ChildrenCTE cte
          INNER JOIN @Data d ON d.ParentID = cte.ID
)
SELECT  d.ID, d.ParentID, d.Text, d.Price, cnt.Children
FROM    @Data d
        INNER JOIN (
          SELECT  ID = RootID, Children = COUNT(*) - 1
          FROM    ChildrenCTE
          GROUP BY RootID
        ) cnt ON cnt.ID = d.ID