code: func (b *builtinLeastIntSig) evalInt(row chunk.Row) (min int64, isNull bool, err error) {
  	min, isNull, err = b.args[0].EvalInt(b.ctx, row)
  	if isNull || err != nil {
  		return min, isNull, err
  	}
  	for i := 1; i < len(b.args); i++ {
  		var v int64
  		v, isNull, err = b.args[i].EvalInt(b.ctx, row)
  		if isNull || err != nil {
  			return min, isNull, err
  		}
  		if v < min {
  			min = v
  		}
  	}
  	return
  }
docs: // evalInt evals a builtinLeastIntSig.
  // See http://dev.mysql.com/doc/refman/5.7/en/comparison-operators.html#functionleast