Module « sqlalchemy »

Fonction tablesample - module sqlalchemy

Signature de la fonction tablesample

def tablesample(selectable, sampling, name=None, seed=None) 

Description

tablesample.__doc__

Return a :class:`_expression.TableSample` object.

        :class:`_expression.TableSample` is an :class:`_expression.Alias`
        subclass that represents
        a table with the TABLESAMPLE clause applied to it.
        :func:`_expression.tablesample`
        is also available from the :class:`_expression.FromClause`
        class via the
        :meth:`_expression.FromClause.tablesample` method.

        The TABLESAMPLE clause allows selecting a randomly selected approximate
        percentage of rows from a table. It supports multiple sampling methods,
        most commonly BERNOULLI and SYSTEM.

        e.g.::

            from sqlalchemy import func

            selectable = people.tablesample(
                        func.bernoulli(1),
                        name='alias',
                        seed=func.random())
            stmt = select(selectable.c.people_id)

        Assuming ``people`` with a column ``people_id``, the above
        statement would render as::

            SELECT alias.people_id FROM
            people AS alias TABLESAMPLE bernoulli(:bernoulli_1)
            REPEATABLE (random())

        .. versionadded:: 1.1

        :param sampling: a ``float`` percentage between 0 and 100 or
            :class:`_functions.Function`.

        :param name: optional alias name

        :param seed: any real-valued SQL expression.  When specified, the
         REPEATABLE sub-clause is also rendered.