What columnns to select in query.
        :column should be a column name or equation to produce column **not** aggregated
        :agg should be a valid aggregate method used to producte the figure
        :_as should be a string used to represent the column. Required when agg present

def select(self, column, agg=None, _as=None, distinct=False):
        """
        What columnns to select in query.
        :column should be a column name or equation to produce column **not** aggregated
        :agg should be a valid aggregate method used to producte the figure
        :_as should be a string used to represent the column. Required when agg present
        """
        if agg and not _as:
            raise ValueError("Aggregate colunns require `_as` to be specified")
        if column is False:
            self._selects = {}
        else:
            self._selects.setdefault((_as or column), (column, agg, _as, distinct))