用CASE方式，方便的把DateTime的空值情况置为Null

strSql = "insert into DebugNote (boardid) values(case when '"+this.txtWorkType.Text.Trim()+"' = '' then null else '"+this.txtWorkType.Text.Trim()+"' end)";
   strSql = "update DebugNote set boardid = case when '"+this.txtWorkType.Text.Trim()+"' = '' then null else '"+this.txtWorkType.Text.Trim()+"' end where debugid =1";