code: func (b *builtinAbsUIntSig) evalInt(row chunk.Row) (int64, bool, error) {
  	return b.args[0].EvalInt(b.ctx, row)
  }
docs: // evalInt evals ABS(value).
  // See https://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_abs