code: func builtinCeil(args []types.Datum, ctx context.Context) (d types.Datum, err error) {
  	if args[0].IsNull() ||
  		args[0].Kind() == types.KindUint64 || args[0].Kind() == types.KindInt64 {
  		return args[0], nil
  	}
  
  	f, err := args[0].ToFloat64(ctx.GetSessionVars().StmtCtx)
  	if err != nil {
  		return d, errors.Trace(err)
  	}
  	d.SetFloat64(math.Ceil(f))
  	return
  }
docs: // See http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_ceiling