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I have query in a stored procedure that calls some linked servers with some dynamic SQL. I understand that EF doesn't like that, so I specifically listed all the columns that would be returned. Yet, it still doesn't like that. What am I doing wrong here? I just want EF to be able to detect the columns returned from the stored procedure so I can create the classes I need.
Please see the following code that makes up the last lines of my stored procedure:
SELECT
#TempMain.ID,
#TempMain.Class_Data,
#TempMain.Web_Store_Class1,
#TempMain.Web_Store_Class2,
#TempMain.Web_Store_Status,
#TempMain.Cur_1pc_Cat51_Price,
#TempMain.Cur_1pc_Cat52_Price,
#TempMain.Cur_1pc_Cat61_Price,
#TempMain.Cur_1pc_Cat62_Price,
#TempMain.Cur_1pc_Cat63_Price,
#TempMain.Flat_Length,
#TempMain.Flat_Width,
#TempMain.Item_Height,
#TempMain.Item_Weight,
#TempMain.Um,
#TempMain.Lead_Time_Code,
#TempMain.Wp_Image_Nme,
#TempMain.Wp_Mod_Dte,
#TempMain.Catalog_Price_Chg_Dt,
#TempMain.Description,
#TempMain.Supersede_Ctl,
#TempMain.Supersede_Pn,
TempDesc.Cust_Desc,
TempMfgr.Mfgr_Item_Nbr,
TempMfgr.Mfgr_Name,
TempMfgr.Vendor_ID
FROM
#TempMain
LEFT JOIN TempDesc ON #TempMain.ID = TempDesc.ID
LEFT JOIN TempMfgr ON #TempMain.ID = TempMfgr.ID
EF doesn't support importing stored procedures which build result set from:
Dynamic queries
Temporary tables
The reason is that to import the procedure EF must execute it. Such operation can be dangerous because it can trigger some changes in the database. Because of that EF uses special SQL command before it executes the stored procedure:
SET FMTONLY ON
By executing this command stored procedure will return only "metadata" about columns in its result set and it will not execute its logic. But because the logic wasn't executed there is no temporary table (or built dynamic query) so metadata contains nothing.
You have two choices (except the one which requires re-writing your stored procedure to not use these features):
Define the returned complex type manually (I guess it should work)
Use a hack and just for adding the stored procedure put at its beginning SET FMTONLY OFF. This will allow rest of your SP's code to execute in normal way. Just make sure that your SP doesn't modify any data because these modifications will be executed during import! After successful import remove that hack.
Adding this Non-Logical block of code solved the problem. Even though it will never Hit
IF 1=0 BEGIN
SET FMTONLY OFF
END
Why does my typed dataset not like temporary tables?
http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataset/thread/fe76d511-64a8-436d-9c16-6d09ecf436ea/
Or you can create a User-Defined Table Type and return that.
CREATE TYPE T1 AS TABLE
( ID bigint NOT NULL
,Field1 varchar(max) COLLATE Latin1_General_CI_AI NOT NULL
,Field2 bit NOT NULL
,Field3 varchar(500) NOT NULL
);
GO
Then in the procedure:
DECLARE #tempTable dbo.T1
INSERT #tempTable (ID, Field1, Field2, Field3)
SELECT .....
....
SELECT * FROM #tempTable
Now EF should be able to recognize the returned columns type.
As some others have noted, make sure the procedure actually runs. In particular, in my case, I was running the procedure happily without error in SQL Server Management Studio completely forgetting that I was logged in with admin rights. As soon as I tried running the procedure using my application's principal user I found there was a table in the query that that user did not have permission to access.
Interesting side note: Had the same problem which I first solved by using Table Variables, rather than Temp Tables (just for the import). That wasn't particularly intuitive to me, and threw me off when initially observing my two SProcs: one using Temp tables and one with Table Variables.
(SET FMTONLY OFF never worked for me, so I just changed my SProcs temporarily to get the column info, rather than bothering with the hack on the EF side just as an FYI.)
My best option was really just manually creating the complex type and mapping the function import to it. Worked great, and the only difference ended up being that an additional FactoryMethod to create the properties was included in the Designer.
What I would add is:
That the import also fails if the stored procedures has parameters and returns no result set for the default parameter values.
My stored procedure had 2 float parameters and would not return anything when both parameters are 0.
So in order to add this stored procedure to the entity model, I set the value of these parameters in the stored procedure so that it is guaranteed to return some rows, no matter what the parameters actually are.
Then after adding this stored procedure to the entity model I undid the changes.
both solutions :
1- Define the returned complex type manually (I guess it should work)
2- Use a hack and just for adding the stored procedure put at its beginning SET FMTONLY OFF.
not working with me in some procedure however it worked with other one!
my procedure ends with this line:
SELECT machineId, production [AProduction]
, (select production FROM #ShiftBFinalProd WHERE machineId = #ShiftAFinalProd.machineId) [BProduction]
, (select production FROM #ShiftCFinalProd WHERE machineId = #ShiftAFinalProd.machineId) [CProduction]
FROM #ShiftAFinalProd
ORDER BY machineId
Thanks
In addition to what #tmanthley said, be sure that your stored procedure actually works by running it first in SSMS. I had imported some stored procedures and forgot about a couple dependent scalar functions, which caused EF to determine that the procedure returned no columns. Seems like a mistake I should have caught earlier on, but EF doesn't give you an error message in that case.
Entity Framework will try to get the columns by executing your stored procedure, passing NULL for every argument.
Please make sure that the stored procedure will return something under all the circumstances. Note it may have been smarter for Entity Framework to execute the stored proc with default values for the arguments, as opposed to NULLs.
ER does the following to get the metadata of the table:
SET FMTONLY ON
This will break your stored procedure in various circumstances, in particular, if it uses a temporary table.
So to get a result as complex type; please try by adding
SET FMTONLY OFF;
This worked for me - hope it works for you too.
Referred from https://social.msdn.microsoft.com/Forums/en-US/e7f598a2-6827-4b27-a09d-aefe733b48e6/entity-model-add-function-import-stored-procedure-returns-no-columns?forum=adodotnetentityframework
In my case adding SET NOCOUNT ON; at the top of the procedure fixed the problem. It's best practice anyway.
In my case SET FMTONLY OFF did not work. The method I followed is, I took backup of original stored procedure and replace with only column name like the below query.
Select Convert(max,'') as Id,Convert(max,'') as Name
After this change, create new function import, complex type in entity framework.
Once the function import and complex type is created, replace the above query with your original stored procedure.
SET FMTONLY OFF
worked for me for one of the procedure but failed for other procedure. Following steps helps me to resolve my problem
Within a stored procedure, I have created temporary table with the same column type and inserted all the data returned by dynamic query to temp table.
and selected the temp table data.
Create table #temp
(
-- columns with same types as dynamic query
)
EXEC sp_executeSQL #sql
insert into #temp
Select * from #temp
drop table #temp
Deleted existing complex type, import function and stored procedure instance for old stored procedure and updated entity model for current new procedure.
Edit the imported Function in entity modal for desired complex type, you will get all the column information there which is not getting for previous stored procedure.
once you have done with the type creation you can delete the temporary table from stored procedure and then refresh Entity Framework.
In Entity framework, while getting column information the sql executes the procedure with passing null values in parameter. So I handled null case differently by creating a temp table with all the required columns and returning all the columns with no value when null is passed to the procedure.
In my procedure there was dynamic query, something like
declare #category_id int
set #category_id = (SELECT CATEGORY_ID FROM CORE_USER where USER_ID = #USER_ID)
declare #tableName varchar(15)
declare #sql VARCHAR(max)
declare #USER_IDT varchar(100)
declare #SESSION_IDT varchar(10)
IF (#category_id = 3)
set #tableName = 'STUD_STUDENT'
else if(#category_id = 4)
set #tableName = 'STUD_GUARDIAN'
if isnull(#tableName,'')<>''
begin
set #sql = 'SELECT [USER_ID], [FIRST_NAME], SCHOOL_NAME, SOCIETY_NAME, SCHOOL_ID,
SESSION_ID, [START_DATE], [END_DATE]
from #tableName
....
EXECUTE (#sql)
END
ELSE
BEGIN
SELECT * from #UserPrfTemp
END
I was not getting the column information in
my case after using the set FMTONLY OFF trick.
This is temp table I created to get the blank data.
Now I am getting the column info
Create table #UserPrfTemp
(
[USER_ID] bigint,
[FIRST_NAME] nvarchar(60),
SCHOOL_NAME nvarchar(60),
SOCIETY_NAME nvarchar(200)
.....
}
I solved this problem creating a table variable and then returning from it.
DECLARE #VarTable TABLE (
NeededColumn1 VARCHAR(100),
NeededColumn2 INT,
NeededColumn3 VARCHAR(100)
)
...
--Fetch Data from Linked server here
...
INSERT INTO #VarTable (NeededColumn1,NeededColumn2,NeededColumn3)
SELECT Column1, Column2, Column3
FROM #TempTable
SELECT * FROM #VarTable.
In that manner, your the SP result will be bounded to the table variable, which EF has access to.
I discovered a method that should help most people out whatever's happening.
Pull up your favourite SQL client and run the proc that you're trying to update with every parameter = null. Visual Studio is literally trying to do this when SET FMTONLY ON. Run a trace. You'll see.
You'll probably get an error, or unexpected data out. Fix that and your issue is fixed.
In my case the function read in JSON and failed because the JSON string was empty.
I just put something like
IF(#FooJSON IS NULL)
BEGIN
SELECT 1 VAR1, 2 VAR2;
END
ELSE
--OTHER LOGIC
That's probably an ugly solution, but I inherited this mess and we don't go into Ravenholm.
Change #Temp tables with WITH SQL EXPRESSION
I have three stored procedures Sp1, Sp2 and Sp3.
The first one (Sp1) will execute the second one (Sp2) and save returned data into #tempTB1 and the second one will execute the third one (Sp3) and save data into #tempTB2.
If I execute the Sp2 it will work and it will return me all my data from the Sp3, but the problem is in the Sp1, when I execute it it will display this error:
INSERT EXEC statement cannot be nested
I tried to change the place of execute Sp2 and it display me another error:
Cannot use the ROLLBACK statement
within an INSERT-EXEC statement.
This is a common issue when attempting to 'bubble' up data from a chain of stored procedures. A restriction in SQL Server is you can only have one INSERT-EXEC active at a time. I recommend looking at How to Share Data Between Stored Procedures which is a very thorough article on patterns to work around this type of problem.
For example a work around could be to turn Sp3 into a Table-valued function.
This is the only "simple" way to do this in SQL Server without some giant convoluted created function or executed sql string call, both of which are terrible solutions:
create a temp table
openrowset your stored procedure data into it
EXAMPLE:
INSERT INTO #YOUR_TEMP_TABLE
SELECT * FROM OPENROWSET ('SQLOLEDB','Server=(local);TRUSTED_CONNECTION=YES;','set fmtonly off EXEC [ServerName].dbo.[StoredProcedureName] 1,2,3')
Note: You MUST use 'set fmtonly off', AND you CANNOT add dynamic sql to this either inside the openrowset call, either for the string containing your stored procedure parameters or for the table name. Thats why you have to use a temp table rather than table variables, which would have been better, as it out performs temp table in most cases.
OK, encouraged by jimhark here is an example of the old single hash table approach: -
CREATE PROCEDURE SP3 as
BEGIN
SELECT 1, 'Data1'
UNION ALL
SELECT 2, 'Data2'
END
go
CREATE PROCEDURE SP2 as
BEGIN
if exists (select * from tempdb.dbo.sysobjects o where o.xtype in ('U') and o.id = object_id(N'tempdb..#tmp1'))
INSERT INTO #tmp1
EXEC SP3
else
EXEC SP3
END
go
CREATE PROCEDURE SP1 as
BEGIN
EXEC SP2
END
GO
/*
--I want some data back from SP3
-- Just run the SP1
EXEC SP1
*/
/*
--I want some data back from SP3 into a table to do something useful
--Try run this - get an error - can't nest Execs
if exists (select * from tempdb.dbo.sysobjects o where o.xtype in ('U') and o.id = object_id(N'tempdb..#tmp1'))
DROP TABLE #tmp1
CREATE TABLE #tmp1 (ID INT, Data VARCHAR(20))
INSERT INTO #tmp1
EXEC SP1
*/
/*
--I want some data back from SP3 into a table to do something useful
--However, if we run this single hash temp table it is in scope anyway so
--no need for the exec insert
if exists (select * from tempdb.dbo.sysobjects o where o.xtype in ('U') and o.id = object_id(N'tempdb..#tmp1'))
DROP TABLE #tmp1
CREATE TABLE #tmp1 (ID INT, Data VARCHAR(20))
EXEC SP1
SELECT * FROM #tmp1
*/
My work around for this problem has always been to use the principle that single hash temp tables are in scope to any called procs. So, I have an option switch in the proc parameters (default set to off). If this is switched on, the called proc will insert the results into the temp table created in the calling proc. I think in the past I have taken it a step further and put some code in the called proc to check if the single hash table exists in scope, if it does then insert the code, otherwise return the result set. Seems to work well - best way of passing large data sets between procs.
This trick works for me.
You don't have this problem on remote server, because on remote server, the last insert command waits for the result of previous command to execute. It's not the case on same server.
Profit that situation for a workaround.
If you have the right permission to create a Linked Server, do it.
Create the same server as linked server.
in SSMS, log into your server
go to "Server Object
Right Click on "Linked Servers", then "New Linked Server"
on the dialog, give any name of your linked server : eg: THISSERVER
server type is "Other data source"
Provider : Microsoft OLE DB Provider for SQL server
Data source: your IP, it can be also just a dot (.), because it's localhost
Go to the tab "Security" and choose the 3rd one "Be made using the login's current security context"
You can edit the server options (3rd tab) if you want
Press OK, your linked server is created
now your Sql command in the SP1 is
insert into #myTempTable
exec THISSERVER.MY_DATABASE_NAME.MY_SCHEMA.SP2
Believe me, it works even you have dynamic insert in SP2
I found a work around is to convert one of the prods into a table valued function. I realize that is not always possible, and introduces its own limitations. However, I have been able to always find at least one of the procedures a good candidate for this. I like this solution, because it doesn't introduce any "hacks" to the solution.
I encountered this issue when trying to import the results of a Stored Proc into a temp table, and that Stored Proc inserted into a temp table as part of its own operation. The issue being that SQL Server does not allow the same process to write to two different temp tables at the same time.
The accepted OPENROWSET answer works fine, but I needed to avoid using any Dynamic SQL or an external OLE provider in my process, so I went a different route.
One easy workaround I found was to change the temporary table in my stored procedure to a table variable. It works exactly the same as it did with a temp table, but no longer conflicts with my other temp table insert.
Just to head off the comment I know that a few of you are about to write, warning me off Table Variables as performance killers... All I can say to you is that in 2020 it pays dividends not to be afraid of Table Variables. If this was 2008 and my Database was hosted on a server with 16GB RAM and running off 5400RPM HDDs, I might agree with you. But it's 2020 and I have an SSD array as my primary storage and hundreds of gigs of RAM. I could load my entire company's database to a table variable and still have plenty of RAM to spare.
Table Variables are back on the menu!
I recommend to read this entire article. Below is the most relevant section of that article that addresses your question:
Rollback and Error Handling is Difficult
In my articles on Error and Transaction Handling in SQL Server, I suggest that you should always have an error handler like
BEGIN CATCH
IF ##trancount > 0 ROLLBACK TRANSACTION
EXEC error_handler_sp
RETURN 55555
END CATCH
The idea is that even if you do not start a transaction in the procedure, you should always include a ROLLBACK, because if you were not able to fulfil your contract, the transaction is not valid.
Unfortunately, this does not work well with INSERT-EXEC. If the called procedure executes a ROLLBACK statement, this happens:
Msg 3915, Level 16, State 0, Procedure SalesByStore, Line 9 Cannot use the ROLLBACK statement within an INSERT-EXEC statement.
The execution of the stored procedure is aborted. If there is no CATCH handler anywhere, the entire batch is aborted, and the transaction is rolled back. If the INSERT-EXEC is inside TRY-CATCH, that CATCH handler will fire, but the transaction is doomed, that is, you must roll it back. The net effect is that the rollback is achieved as requested, but the original error message that triggered the rollback is lost. That may seem like a small thing, but it makes troubleshooting much more difficult, because when you see this error, all you know is that something went wrong, but you don't know what.
I had the same issue and concern over duplicate code in two or more sprocs. I ended up adding an additional attribute for "mode". This allowed common code to exist inside one sproc and the mode directed flow and result set of the sproc.
what about just store the output to the static table ? Like
-- SubProcedure: subProcedureName
---------------------------------
-- Save the value
DELETE lastValue_subProcedureName
INSERT INTO lastValue_subProcedureName (Value)
SELECT #Value
-- Return the value
SELECT #Value
-- Procedure
--------------------------------------------
-- get last value of subProcedureName
SELECT Value FROM lastValue_subProcedureName
its not ideal, but its so simple and you don't need to rewrite everything.
UPDATE:
the previous solution does not work well with parallel queries (async and multiuser accessing) therefore now Iam using temp tables
-- A local temporary table created in a stored procedure is dropped automatically when the stored procedure is finished.
-- The table can be referenced by any nested stored procedures executed by the stored procedure that created the table.
-- The table cannot be referenced by the process that called the stored procedure that created the table.
IF OBJECT_ID('tempdb..#lastValue_spGetData') IS NULL
CREATE TABLE #lastValue_spGetData (Value INT)
-- trigger stored procedure with special silent parameter
EXEC dbo.spGetData 1 --silent mode parameter
nested spGetData stored procedure content
-- Save the output if temporary table exists.
IF OBJECT_ID('tempdb..#lastValue_spGetData') IS NOT NULL
BEGIN
DELETE #lastValue_spGetData
INSERT INTO #lastValue_spGetData(Value)
SELECT Col1 FROM dbo.Table1
END
-- stored procedure return
IF #silentMode = 0
SELECT Col1 FROM dbo.Table1
Declare an output cursor variable to the inner sp :
#c CURSOR VARYING OUTPUT
Then declare a cursor c to the select you want to return.
Then open the cursor.
Then set the reference:
DECLARE c CURSOR LOCAL FAST_FORWARD READ_ONLY FOR
SELECT ...
OPEN c
SET #c = c
DO NOT close or reallocate.
Now call the inner sp from the outer one supplying a cursor parameter like:
exec sp_abc a,b,c,, #cOUT OUTPUT
Once the inner sp executes, your #cOUT is ready to fetch. Loop and then close and deallocate.
If you are able to use other associated technologies such as C#, I suggest using the built in SQL command with Transaction parameter.
var sqlCommand = new SqlCommand(commandText, null, transaction);
I've created a simple Console App that demonstrates this ability which can be found here:
https://github.com/hecked12/SQL-Transaction-Using-C-Sharp
In short, C# allows you to overcome this limitation where you can inspect the output of each stored procedure and use that output however you like, for example you can feed it to another stored procedure. If the output is ok, you can commit the transaction, otherwise, you can revert the changes using rollback.
On SQL Server 2008 R2, I had a mismatch in table columns that caused the Rollback error. It went away when I fixed my sqlcmd table variable populated by the insert-exec statement to match that returned by the stored proc. It was missing org_code. In a windows cmd file, it loads result of stored procedure and selects it.
set SQLTXT= declare #resets as table (org_id nvarchar(9), org_code char(4), ^
tin(char9), old_strt_dt char(10), strt_dt char(10)); ^
insert #resets exec rsp_reset; ^
select * from #resets;
sqlcmd -U user -P pass -d database -S server -Q "%SQLTXT%" -o "OrgReport.txt"
Is there a way via metadata (Information_Schema, perhaps?) to get a list of the columns a sproc will return? I'm trying to automate some code generation and that would help tremendously...
Unless you're prepared to parse the contents of ROUTINE_DEFINITION in INFORMATION_SCHEMA.ROUTINES, then your best bet will be to execute the procedures, and read the column information from the records returned.
In .NET you can do this by reading the results of the stored procedure into a DataTable and querying the Columns property.
The reason there's no easy way to do this is a stored procedure could potentially return different result sets based on the parameters. There's no fixed result set format like there is with user defined functions.
Edit
As mentioned in the other answer, you will need to use SET FMTONLY ON to ensure no data is returned. There are some situations where SET FMTONLY won't work, e.g. when using #temp tables in your stored procedures, but there is a workaround.
I just ran Profiler to see how Visual Studio does this for the strongly typed dataset drag and drop.
This is the code it sent.
SET NO_BROWSETABLE ON;
SET FMTONLY ON;
exec dbo.aspnet_Roles_GetAllRoles #ApplicationName=NULL
So I presume there might not be any "more official" way of doing it.
Obviously you would need to bear in mind that a single stored procedure might return multiple result sets or different result sets dependant on the parameters passed.
For people on 2012+ another approach might be to use sp_describe_first_result_set
My way of doing this:
Edit the stored procedure to have an INTO clause:
Change
Select * from tablename
to
Select * INTO _tablename FROM tablename
This creates a table in the database.
Then, use SELECT * FROM INFORMATION_SCHEMA WHERE TABLE_NAME = '_tablename'
Don't forget to undo the modification to the sproc.
I have a stored procedure for SQL Server 2000 that can only have a single instance being executed at any given moment. Is there any way to check and ensure that the procedure is not currently in execution?
Ideally, I'd like the code to be self contained and efficient (fast). I also don't want to do something like creating a global temp table checking for it's existence because if the procedure fails for some reason, it will always be considered as running...
I've searched, I don't think this has been asked yet. If it has been, sorry.
yes there is a way. use what is known as SQL Server Application locks.
EDIT: yes this also works in SQL Server 2000.
You can use sp_getapplock sp_releaseapplock as in the example found at Lock a Stored Procedure for Single Use Only.
But, is that what you are really trying to do? Are you trying to get a transaction with a high isolation level? You would also likely be much better off handling that type of concurrency at the application level as in general higher level languages have much better primitives for that sort of thing.
how about locking a dummy table? That wouldn't cause deadlocks in case of failures.
One of the initial external links shared in the replies had helpful info but personally I prefer for standalone answers/snippets to be right here on the Stack Overflow question page. See below snippet for what I used and solved my (similar) problem. If anyone has problems (or adjustment suggestions) please chime in.
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[MyLockedAndDelayedStoredProcedure]') AND type in (N'P', N'PC'))
DROP PROCEDURE [GetSessionParticipantAnswersFromEmailAddressAndSessionName]
GO
CREATE PROCEDURE [MyLockedAndDelayedStoredProcedure]
#param1 nvarchar(max) = ''
AS
BEGIN
DECLARE #LockedTransactionReturnCode INT
PRINT 'MyLockedAndDelayedStoredProcedure CALLED at ' + CONVERT(VARCHAR(12),GETDATE(),114);
BEGIN TRANSACTION
EXEC #LockedTransactionReturnCode =sp_getapplock #Resource='MyLockedAndDelayedStoredProcedure_LOCK', #LockMode='Exclusive', #LockOwner='Transaction', #LockTimeout = 10000
PRINT 'MyLockedAndDelayedStoredProcedure STARTED at ' + CONVERT(VARCHAR(12),GETDATE(),114);
-- Do your Stored Procedure Stuff here
Select #param1;
-- If you don't want/need a delay remove this line
WAITFOR DELAY '00:00:3'; -- 3 second delay
PRINT 'MyLockedAndDelayedStoredProcedure ENDED at ' + CONVERT(VARCHAR(12),GETDATE(),114);
COMMIT
END
-- https://gist.github.com/cemerson/366358cafc60bc1676f8345fe3626a3f
At the start of the procedure check if piece of data is 'locked' if not lock it
At end of procedure unlock the piece of data.
ie
SELECT #IsLocked=IsLocked FROM CheckLockedTable Where spName = 'this_storedProcedure'
IF #IsLocked = 1
RETURN
ELSE
UPDATE CheckLockedTable SET IsLocked = 1 Where spName = 'this_storedProcedure'
.
.
.
-- At end of Stored Procedure
UPDATE CheckLockedTable SET IsLocked = 0 Where spName = 'this_storedProcedure'
I've got a search screen on which the user can specify any combination of first name, last name, semester, or course. I'm not sure how to optimally code the SQL Server 2005 stored procedure to handle these potentially optional parameters. What's the most efficient way? Separate procedures for each combination? Taking the items in as nullable parms and building dynamic SQL?
I'd set each parameter to optional (default value being null)
and then handle it in the WHERE....
FirstName=ISNULL(#FirstName,FirstName)
AND
LastName=ISNULL(#LastName,LastName)
AND
SemesterID=ISNULL(#SemesterID,SemesterID)
That'll handle only first name, only last name, all three, etc., etc.
It's also a lot more pretty/manageable/robust than building the SQL string dynamically and executing that.
The best solution is to utilize sp_execute_sql. For example:
--BEGIN SQL
declare #sql nvarchar(4000)
set #sql =
'select * from weblogs.dbo.vwlogs
where Log_time between #BeginDate and #EndDate'
+ case when #UserName is null then '' else 'and client_user = #UserName' end
sp_execute_sql
#sql
, #params = '#UserName varchar(50)'
, #UserName = #UserName
--END SQL
As muerte mentioned, this will have a performance benefit versus exec()'ing a similar statement.
I would do it with sp_executesql because the plan will be cached just for the first pattern, or the first set of conditions.
Take a look at this TechNet article:
sp_executesql can be used instead of stored procedures to execute a Transact-SQL statement many times when the change in parameter values to the statement is the only variation. Because the Transact-SQL statement itself remains constant and only the parameter values change, the SQL Server query optimizer is likely to reuse the execution plan it generates for the first execution.
Was just posting the same concept as Kevin Fairchild, that is how we typically handle it.
You could do dynamic sql in your code to create the statement as required but if so you need to watch for sql injection.
As muerte points out, the plan will be cached for the first set of parameters. This can lead to bad performance when its run each subsequent time using alternate parameters. To resolve that use the WITH RECOMPILE option on the procedure.