mysql date time format using c#

You're going wrong by trying to include a value directly in your SQL query to start with. Use parameterized SQL and specify the value as a DateTime, and assuming your database table is also using a date/datetime field (which it should be), you should be fine.

You should avoid including values directly in your SQL for three reasons:

• You'll end up with troublesome string conversions which can use inappropriate formats etc. That's the problem here.
• You're inviting SQL injection attacks
• You're mixing code and data, which makes it harder to read the code and harder to check the data

You want something like:

string sql = @"Select distinct v.* from Ven v 
               inner join Des d on v.venid=d.venid 
               and cast(d.despdate as datetime) between @start and @end";
using (MySqlCommand command = new MySqlCommand(connection, sql))
{
    command.Parameters.AddWithValue("@start", startDateTime);
    command.Parameters.AddWithValue("@end", endDateTime);
    // Execute the command here
}

If Des.despdate isn't already a suitable data type, you should change that...

convert your column d.despdate into DATE using STR_TO_DATE

SELECT  ...
FROM    ...
WHERE   STR_TO_DATE(d.despdate, '%d-%b-%Y') BETWEEN '2013-01-15' AND '2013-01-30'

for better performance, parameterized the query using MySQLCommand object. ex,

string connStr = "connection string here";
string query = @"SELECT ... 
                FROM... 
                WHERE STR_TO_DATE(d.despdate, '%d-%b-%Y') BETWEEN @date1 AND @date2"
using(MySqlConnection _conn = new MySqlConnection(connStr))
{
    using (MySqlCommand comm = new MySqlCommand())
    {
        comm.Connection = conn;
        comm.CommandText = query;
        comm.Parameters.AddWithValue("@date1", dTime1.Value);
        comm.Parameters.AddWithValue("@date2", dTime2.Value);
        try
        {
            conn.Open();
            comm.ExecuteNonQuery();
        }
        catch(MySqlException e)
        {
            // do something with
            // e.ToString()
        }
    }
}

It should be yyyy

 Select distinct v.* from Ven v inner join Des d on v.venid=d.venid and cast( d.despdate as datetime) between  cast('" + dTime1.Value.ToString("dd-MMM-yyyy") + "' as datetime) and cast('" + dTime2.Value.ToString("dd-MMM-yyyy") + "'as datetime)