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Archive for March, 2009

SSIS Execute Task Failure

Possible failure reasons: Problems with the query, “ResultSet” property not set correctly, parameters not set correctly, or connection not established correctly.

Every so often ETL developers working with the Execute SQL Task in SSIS encounter the error above. I have seen a few developers who try to ‘quick-fix’ this by changing type mappings without exactly knowing the differences between them and re-running the ETL task only to get to the next red light. The best example of this would be the type mismatch of Long and Numeric types when using the native OLEDB provider. I wouldn’t be surprised if there are developers out there looking up the precision error on the types. I will not delve too deep into all the providers, but will provide a reference to a very good resource that Microsoft has provided, and which I think should be on every ETL developer’s desk.

In this (first) blog I will point out the most common places in the Execute SQL Task where you should troubleshoot the error (above). Will also go over some SQL provider information at a high level.

Steps to troubleshoot the ‘Execute SQL Task’ error (order need not be followed):

1. Verify that for the stored procedure\SQL statement used, the parameter counts and direction (input, output or return value) is set appropriately.

If using a OLEDB or ODBC provider check if your number of “?” (parameters), and if using ADO or ADO.NET provider, check the number of @ are equal to the number of parameters being mapped to on the parameter mapping screen.

2. Verify your data types.

Verify that the data types that exist\declared in the stored procedure or SQL are mapped to a compatible data type in the parameter mapping. For example: when using the OLEDB provider, map the integer (int) parameters to Long data type.

Providers: Which data provider should be used when choosing between (Managed) ADO.NET or (Native) OLEDB? – There are n number of websites and blogs (yes, this is also another one of them) which will tell you why you should prefer the use of OLEDB provider over ADO.NET, as ADO.NET is a managed provider which adds another layer code to connect to the data source, thus making ADO.NET slower than OLEDB. If you really want to find the exact runtime exection difference I would suggest running profiler with the two connection managers and then comparing them.

Helpful links for data type mapping and provider info:
http://msdn.microsoft.com/en-us/library/aa198346(SQL.80).aspx
http://msdn.microsoft.com/en-us/library/aa263420.aspx
http://www.carlprothman.net/Default.aspx?tabid=97#10

3. Verify the ResultSet property:

Verify that the ResultSet property is set appropriately for the SQL command being executed. For example: if the SQL command\stored procedure returns a full result set, set it to the ‘Object’ data type, so that you can retrieve from the object based on the index position of the result (0 = first column, 1 = second column and so on) as members of the ‘Object’ type are ordinal. Also make sure that all columns in the sql result set have column names.

4. Do you trust your SQL Command\Stored procedure, there is a very good possibilty if it being incorrect:

The execute SQL task can do nothing about bad\erroneous SQL code given to it for execution but fail it. As a routine, test the SQL for all possible exceptions, giving more importance to situations where a value or a list of values is expected and nothing is returned.

For example: the sub query inside the stored procedure may be returning multiple values, NULL\invalid or no values at all. Watch out for the tricky no value situation.

Example: In this example, our objective is to retrieve object_id from sys.objects where the name meets a certain condition. The ‘ResultSet’ property of the execute sql task is being set to “Single Row” (as our objective is to retrieve a scalar value).

[Note: Each Case builds on the previous cases.]

Case 1: Simple Select to assign to a variable

SELECT object_id FROM sys.objects WHERE name = ‘sysrowsets’;

 

If the result set of the execute sql task is set to “Single Row”, it will work only when the WHERE condition is satisfied. If it is not satisfied, it does not return NULL, instead returns nothing, i.e. an empty result set; which will cause the task to fail giving us the same error “ResultSet property not set correctly“. [A developer must keep this exception in mind when testing the execute sql task]. This query will also raise an exception when multiple values are returned by the query and our task is to assign a single value to a variable from the output of our query.

Case 2: Handle multiple values.

DECLARE @Object_ID int;


SET @Object_ID = (SELECT TOP 1 object_id FROM sys.objects WHERE name = ‘sysrowsets’);

 

In this case, we handled the multiple values problem from Case1. Now, if the result set returns anything other than a NULL value or a Non-Empty value, we are close to living in a perfect world, but, as it turns out (someone told me) that we don’t. If\When a NULL or an empty result is returned by the above query an exception will be thrown. Yes; it is the same exception we are discussing in this article.

I am more inclined on the ‘When’ it will happen than the ‘if’ possibility because at-least in the scenarios I have worked with, it was bound to happen, then again, your case may be different.

Case 3: Split the simple select into ‘simpler’ select.

DECLARE @Object_ID int;


SET @Object_ID = (SELECT TOP 1 object_id FROM sys.objects WHERE name = ‘sysrowsets_Bogus);


//Comments-The _Bogus makes the query to return an empty result set.


SELECT ISNULL(@Object_ID, 0) AS ‘Object_ID’;

 

The first Select statement here takes care of multiple values; the second Select statement handles any NULL values and sets it to 0 and also solves the ’empty’ result set problem when the @Object_ID is selected separately in a different query (as the 2nd query).

Summary

To summarize, double check your SQL queries\Stored procedures before you execute them in the ExecuteSQLTask. Don’t jump to hasty conclusions about the error message description Integration Services provides you. For instance if you get any ‘Arithabort error’ [Ex: Update failed because the following SET options have incorrect settings: ‘ARITHABORT’] on a stored procedure that performs an insert\update\delete – check the database compatibility level (sp_dbcmptlevel) which maybe a SQL Server 2000 database with setting 80 and needs to be upgraded to compatibility level 90 of SQL Server 2005, or verify if any columns are computed columns performing calculations which may be throwing arithabort errors. Check for any external factors that are affecting your ExecuteSQLTask variables, for instance package configurations or dynamic expressions. Performing these checks will surely save you some time in the long run and also make your packages robust.

Hope this article\blog was helpful. Do leave a feedback (as this is my first blog). My next blog is about enumerating Reporting Services metadata from models into a database repository. Hope to get it out soon.

Thanks,

Vishal Gamji

MCITP – Database Developer

admin@expertsqltraining.com