How to Use 'Like' with a parameter

Question

I want to search for a number embedded in a string in a field in our log table using a parameter.

select * from vwLogs where log_time >\'02/24/2009\' and message lik

Answer 1

WHERE message like '%' + @ErrorMessage + '%'

Based on your edit I don't immediately see what's causing your error, but I did spot two potential issues:

1. It's not handling null ErrorNumbers correctly. I don't think this is it, because an empty string should still match everything for that query. But fixing the nulls will improve performance for that case.
2. It's treating it as a numeric type rather than a varchar. This also has performance implications and might actually break the LIKE query: I don't recall what the behavior is off the top of my head.

Try this:

protected void btnRunQuery_Click(object sender, EventArgs e)
{
    string strConn = @";";
    string strSQL =
         "SELECT * "
      + " FROM weblogs.dbo.vwlogs"
      + " WHERE Log_time >= @BeginDate AND Log_Time < @EndDate"
          + " AND (client_user=@UserName OR @UserName IS NULL)" 
          + " AND (message like '%' + @ErrorNumber + '%' OR @ErrorNumber IS NULL)"
      + " ORDER BY Log_time DESC";

    using (SqlConnection cn = new SqlConnection(strConn))
    using (SqlCommand cmd = new SqlCommand(strSQL, cn))
    {
        cmd.Parameters.Add("@BeginDate", SqlDbType.DateTime).Value =
            DateTime.Parse(txtBeginDate.Text).Date;
        cmd.Parameters.Add("@EndDAte", SqlDbType.DateTime).Value =
            // add one to make search inclusive
            DateTime.Parse(txtEndDate.Text).Date.AddDays(1);
        cmd.Parameters.Add("@UserName", SqlDbType.VarChar, 50).Value = 
            string.IsNullOrEmpty(txtUserName.Text) ? DBNull.Value : txtUserName.Text;
        cmd.Parameters.Add("@ErrorNumber", SqlDbType.VarChar, 50).Value =
            string.IsNullOrEmpty(txtErrorNumber.Text) ? DBNull.Value : txtErrorNumber.Text;

        cn.Open();
        SqlDataReader rdr = cmd.ExecuteReader();

        GridView1.DataSource = rdr;
        GridView1.DataBind();
    }
}

BTW: didn't I give you that code in the first place? :)