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Posted 5 Oct 2009

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How to Create T-SQL CASE Statements With LINQ To SQL

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5 Oct 2009CPOL
How to create T-SQL CASE statements with LINQ to SQL

I was recently asked to help with a LINQ To SQL query where the resulting T-SQL query was to have CASE statements. Having CASE statements in T-SQL queries is a common scenario but how do we it in LINQ to SQL? The solution is simple and straight-forward. As you will see below, using C#'s "Immediate If" will convert into T-SQL CASE statements.

I have created a table called CityWeather. This table has two fields: Name and Temperature. Here is the script if you wish to create the table on your machine.

CREATE TABLE [dbo].[CityWeather](
[Name] [nvarchar](100) NOT NULL,
[Temperature] [decimal](18, 0) NOT NULL

My objective is to get LINQ To SQL to produce a T-SQL statement similar to this:

CASE Temperature
WHEN 30 THEN 'Toasted'
WHEN 25 THEN 'I like it'
WHEN 10 THEN 'Just perfect'
WHEN -15 THEN 'Gonna freeze my'
END AS 'Message'
FROM CityWeather

Below is the C# code I wrote for my LINQ To SQL query:

from c in CityWeathers
select new
          Messaage = c.Temperature == 30 ? "Toasted" : 
          c.Temperature == 25 ? "I like it" :
          c.Temperature == 10 ? "Just perfect" :
          c.Temperature == -15 ? "Gonna freeze my" : ""

My LINQ To SQL query produced the following T-SQL Query:

SELECT [t0].[Name], [t0].[Temperature],
WHEN [t0].[Temperature] = @p0 THEN CONVERT(NVarChar(15),@p1)
WHEN [t0].[Temperature] = @p2 THEN CONVERT(NVarChar(15),@p3)
WHEN [t0].[Temperature] = @p4 THEN CONVERT(NVarChar(15),@p5)
WHEN [t0].[Temperature] = @p6 THEN @p7
ELSE CONVERT(NVarChar(15),@p8)
END) AS [Messaage]
FROM [CityWeather] AS [t0]
-- @p0: Input Decimal (Size = 0; Prec = 33; Scale = 4) [30]
-- @p1: Input NVarChar (Size = 7; Prec = 0; Scale = 0) [Toasted]
-- @p2: Input Decimal (Size = 0; Prec = 33; Scale = 4) [25]
-- @p3: Input NVarChar (Size = 9; Prec = 0; Scale = 0) [I like it]
-- @p4: Input Decimal (Size = 0; Prec = 33; Scale = 4) [10]
-- @p5: Input NVarChar (Size = 12; Prec = 0; Scale = 0) [Just perfect]
-- @p6: Input Decimal (Size = 0; Prec = 33; Scale = 4) [-15]
-- @p7: Input NVarChar (Size = 15; Prec = 0; Scale = 0) [Gonna freeze my]
-- @p8: Input NVarChar (Size = 0; Prec = 0; Scale = 0) []
-- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 3.5.30729


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By
Software Developer (Senior)
United States United States
Winner - Best Mobile App - AT&T Developer Summit, Las Vegas, 2013

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About Philip Pierce:

I am a software developer with twenty years experience in game development, mobile, web, desktop, server, and database. My extensive background highlights an expertise in rapid application development using the latest Microsoft, Mobile, and Game Development technologies, along with the ability to create AI for games and business software, redesign existing software, develop multi-threaded software, and create client/server applications.

Comments and Discussions

QuestionPreviewing the previous month of the selected month and the selected month Pin
qwerzxcxyz12-Jul-15 21:48
professionalqwerzxcxyz12-Jul-15 21:48 
QuestionUsing Orderby clause to the statement Pin
jibin.mn3-Apr-12 20:31
jibin.mn3-Apr-12 20:31 

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