LINQ Query Expressions C# example

C# > LINQ Query Expressions

Language-Integrated Query (LINQ) is the name for a set of technologies of .NET Framework. This component adds data query  capabilities directly into the C# language.
LINQ expressions are like SQL statements  and can be used to extract and process data from arrays, classes, XML and databases.

Data Source - Query Expression - Execute

Methods

• Single
• FirstOrDefault
• Take
• Join
• Where
• Average

Examples

Example 1.  Fundamental query concepts

            // data source

            int[] int_array = new int[] { 5, 4, 2, 8, 10 };

            // query expression

            IEnumerable<int> intQuery =
                from int_v in int_array
                where int_v >= 5
                select int_v;

            // Execute the query
            foreach (int i in intQuery)
            {
                MessageBox.Show(i.ToString());
            } 
    
Example 2. Order by query

            IEnumerable<int> intQuery =
                from int_v in int_array
                where int_v >= 5
                orderby int_v ascending
                select int_v;

Example 3. Implement RANK function

Example 4. IsNumeric

Example 5. Order By Key Dictionary


         

sp_columns SQL Server example

SQL Server > System Stored Procedures   > sp_columns

sp_columns returns column information for the specified object

Example

create table tmp_Sales(ProductId int, [Year] int, Country varchar(100))
EXEC sp_columns @table_name = N'tmp_Sales'
drop table tmp_Sales

Result:

PIVOT SQL Server Example

SQL Server  > Operators > PIVOT

PIVOT rotates a values from a table by turning the unique values from one column into multiple columns in the output (cross-tab). Also performs aggregations where they are required.

Example:

1.Using PIVOT to get number of product sales

create table #Sales(ProductId int, [Year] int, Country varchar(100))

insert into #Sales(ProductId, [Year], Country  ) values  (1,2012,'Germany'), (1,2012,'UK') , (1,2013,'France') , (2,2013,'Germany')  , (2,2013,'Germany')  , (2,2013,'UK')

SELECT

       Country, [2012], [2013]
FROM
       (SELECT ProductId, [Year], Country FROM #Sales) p
       PIVOT
       (
              COUNT (ProductId)
              FOR [Year] IN ( [2012], [2013] )
       ) AS pvt
ORDER BY pvt.Country ;

drop table #Sales

Result:



2. Dynamic PIVOT and cross-tab query

Create Local temporary table in SQL Server

SQL Server  > Temporary table > Create

Use # character in front of table name to create local temporary table

Example: Create temporary table #user

create table #user(id int, superiorid int)
insert into #user(id, superiorid)
values (1,null), (2,1) , (3,1)
drop table #user

Visual Basic run-time member functions

VB.NET  > Run-time member functions

AppActivate	Asc	AscW	Beep
CallByName	CBool	CByte	CChar
CDate	CDbl	CDec	ChDir
ChDrive	Choose	Chr	ChrW
CInt	CLng	CObj	Command
CreateObject	CShort	CSng	CStr
CType	CurDir

DateAdd	DateDiff	DatePart	DateSerial
DateValue	Day	DDB	DeleteSetting
Derived Math	Dir	Environ	EOF
ErrorToString	FileAttr	FileClose	FileCopy
FileDateTime	FileGet	FileGetObject	FileLen
FileOpen	FilePut	FilePutObject	FileWidth
Filter	Fix	Format	FormatCurrency
FormatDateTime	FormatNumber	FormatPercent	FreeFile
FV	GetAllSettings	GetAttr	GetChar
GetException	GetObject	GetSetting

What is Visual Basic .NET

Visual Basic .NET is the result of a significant rebuild of Visual Basic for the Microsoft .NET Framework.
Visual Basic .NET gives you access to system resources that in the past required the use of languages like C++. One of the most important additions is object inheritance.

• System 
• Run time functions
• Object-Oriented Programming
• Form
• Statements

RANK and DENSE_RANK SQL Server

SQL Server > Built-in Functions > RANK & DENSE_RANK

RANK returns the rank of each row within the partition of a result set

DENSE_RANK returns the rank of rows within the partition of a result set  without any gaps in the ranking

                    OVER ( [ PARTION BY ] [ORDER BY]) 
Example:

CREATE TABLE #LocalTempTable(

       ID            int,
       Name   varchar(50),
       Salary int,
       DeptId int)

insert into #LocalTempTable(Id, Name, Salary, DeptId) values (1,'p1',100,1),  (2,'p2',200,1) ,  (3,'p3', 100,1) ,   (2,'p4', 50,2)

 

--see image 1

select * from #LocalTempTable

--see image 2

SELECT i.*

    ,RANK() OVER
    ( ORDER BY i.Salary DESC) AS Rank
FROM
       #LocalTempTable i
ORDER BY i.DeptId;

--see image 3

SELECT i.*

    ,RANK() OVER
    (PARTITION BY i.DeptId  ORDER BY i.Salary DESC) AS Rank
FROM
       #LocalTempTable i
ORDER BY i.DeptId;

--see image 4

SELECT i.*

    ,DENSE_RANK() OVER
    ( ORDER BY i.Salary DESC) AS Rank
FROM
       #LocalTempTable i
ORDER BY i.DeptId;

drop table #LocalTempTable

Results:

 

Image 1 Salary Data

Image 2 RANK without PARTITION BY will rank all rows. Note the gap between 2 and 4

Image 3 RANK with PARTITION BY will rank rows in the same DeptID.

Image 2 DENSE_RANK  Note there are not gaps