code: func (col *Column) EvalTime(ctx sessionctx.Context, row chunk.Row) (types.Time, bool, error) {
  	if row.IsNull(col.Index) {
  		return types.Time{}, true, nil
  	}
  	return row.GetTime(col.Index), false, nil
  }
docs: // EvalTime returns DATE/DATETIME/TIMESTAMP representation of Column.