Hi there

I found a starnage behavior. I have a method 'GetDataFromDB', which i use
internaly in my class to get data from the db. Now if i build the query
using SqlParameters for the date my query takes up to 60 sec vs. 2 sec if I
do not work with the SqlParameters!

What can be the problem? Did anyone of you had the same problems?

SQL-Statement with DateTime-params:
SELECT @TitleID AS TitleID, StationID, COUNT(*) AS BroadcastCount
FROM tPrg WHERE TitleID = @TitleID
AND StartTime >= @DateFrom
AND StartTime < @DateUntil
GROUP BY StationID ORDER BY StationID


SQL-Statement without DateTime-params:
SELECT @TitleID AS TitleID, StationID, COUNT(*) AS BroadcastCount
FROM tPrg WHERE TitleID = @TitleID
AND StartTime >= CONVERT(DATETIME, '2007-01-1 03:00:00', 102)
AND StartTime < CONVERT(DATETIME, '2007-02-28 03:00:00', 102)
GROUP BY StationID ORDER BY StationID

The implementation of the mentioned method:

public DataTable GetDataFromDB(string sqlStatement, string tableName)
{
DataSet ds = new DataSet();
ValidateConnection();
_dbCommand.CommandType = CommandType.Text;
_dbCommand.CommandText = sqlStatement;
DbDataAdapter adap = _provider.CreateDataAdapter();
adap.SelectCommand = _dbCommand;
adap.Fill(ds);
ds.Tables[0].TableName = tableName;
return ds.Tables[0];
}

Any ideas? Thank you very much for your help!
Jonas

This is relatively common for date range queries on large tables.  When you
use parameters, SQL Server will create a query plan that can be reused for
whatever values of @DateFrom and @DateUntil you pass, and it has no idea how
many days will be contained in that range.  Hard-Coding the parameters will
prevent plan caching and provide SQL Server with more statistical
information on how to execute the query.

You can either use the hard-coded version, or (for SQL 2005) use a query
hint to provide representitive parameter values to "OPTIMIZE FOR".  See

Forcing Query Plans
http://www.microsoft.com/technet/prodtechnol/sql/2005/frcqupln.mspx

Query Hint (Transact-SQL)
http://msdn2.microsoft.com/en-us/library/ms181714.aspx

Batch Compilation, Recompilation, and Plan Caching Issues in SQL Server 2005
http://www.microsoft.com/technet/prodtechnol/sql/2005/recomp.mspx

David

Hi David!

Thank you very much for the fast and good answer!

Jonas

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