sqlalchemy.sql.expression.TableSample

class documentation

class TableSample(AliasedReturnsRows):

Represent a TABLESAMPLE clause.

This object is constructed from the _expression.tablesample module level function as well as the _expression.FromClause.tablesample method available on all _expression.FromClause subclasses.

New in version 1.1.

See Also

_expression.tablesample

Class Method	`_factory`	Return a `_expression.TableSample` object.
Method	`_get_method`	Undocumented
Method	`_init`	Undocumented
Class Variable	`__visit_name__`	Undocumented
Class Variable	`_traverse_internals`	Undocumented
Instance Variable	`sampling`	Undocumented
Instance Variable	`seed`	Undocumented

Inherited from AliasedReturnsRows:

Method	`is_derived_from`	Return `True` if this `_expression.FromClause` is 'derived' from the given `FromClause`.
Class Method	`_construct`	Undocumented
Method	`_copy_internals`	Reassign internal elements to be clones of themselves.
Method	`_populate_column_collection`	Called on subclasses to establish the .c collection.
Method	`_refresh_for_new_column`	Given a column added to the .c collection of an underlying selectable, produce the local version of that column, assuming this selectable ultimately should proxy this column.
Class Variable	`_is_from_container`	Undocumented
Class Variable	`_supports_derived_columns`	Undocumented
Class Variable	`named_with_column`	Undocumented
Instance Variable	`_orig_name`	Undocumented
Instance Variable	`element`	Undocumented
Instance Variable	`name`	Undocumented
Property	`_from_objects`	Undocumented
Property	`bind`	Undocumented
Property	`description`	A brief description of this `_expression.FromClause`.
Property	`original`	Legacy for dialects that are referring to Alias.original.

Inherited from NoInit (via AliasedReturnsRows):

Method __init__ Undocumented

Inherited from FromClause (via AliasedReturnsRows):

Method	`alias`	Return an alias of this `_expression.FromClause`.
Method	`join`	Return a `_expression.Join` from this `_expression.FromClause` to another `FromClause`.
Method	`outerjoin`	No summary
Method	`select`	Return a SELECT of this `_expression.FromClause`.
Method	`table_valued`	Return a `_sql.TableValuedColumn` object for this `_expression.FromClause`.
Method	`tablesample`	Return a TABLESAMPLE alias of this `_expression.FromClause`.
Class Variable	`c`	Undocumented
Class Variable	`schema`	Define the 'schema' attribute for this `_expression.FromClause`.
Instance Variable	`foreign_keys`	Return the collection of `_schema.ForeignKey` marker objects which this FromClause references.
Instance Variable	`primary_key`	Return the iterable collection of `_schema.Column` objects which comprise the primary key of this `_selectable.FromClause`.
Method	`_anonymous_fromclause`	Undocumented
Method	`_generate_fromclause_column_proxies`	Undocumented
Method	`_init_collections`	Undocumented
Method	`_is_lexical_equivalent`	Return `True` if this `_expression.FromClause` and the other represent the same lexical identity.
Method	`_reset_column_collection`	Reset the attributes linked to the `FromClause.c` attribute.
Class Variable	`_hide_froms`	Undocumented
Class Variable	`_is_from_clause`	Undocumented
Class Variable	`_is_join`	Undocumented
Class Variable	`_select_iterable`	Undocumented
Class Variable	`_use_schema_map`	Undocumented
Class Variable	`is_selectable`	Undocumented
Instance Variable	`_columns`	Undocumented
Property	`_cols_populated`	Undocumented
Property	`columns`	A named-based collection of `_expression.ColumnElement` objects maintained by this `_expression.FromClause`.
Property	`entity_namespace`	Return a namespace used for name-based access in SQL expressions.
Property	`exported_columns`	A `_expression.ColumnCollection` that represents the "exported" columns of this `_expression.Selectable`.

Inherited from FromClauseRole (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole):

Class Variable	`_is_subquery`	Undocumented
Class Variable	`_role_name`	Undocumented

Inherited from AllowsLambdaRole (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole, FromClauseRole, ColumnsClauseRole):

Class Variable allows_lambda Undocumented

Inherited from UsesInspection (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole, FromClauseRole, ColumnsClauseRole):

Class Variable	`_post_inspect`	Undocumented
Class Variable	`uses_inspection`	Undocumented

Inherited from SQLRole (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole, FromClauseRole, ColumnsClauseRole, ColumnListRole):

Class Variable	`allows_lambda`	Undocumented
Class Variable	`uses_inspection`	Undocumented

Inherited from AllowsLambdaRole (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole, FromClauseRole, JoinTargetRole):

Class Variable allows_lambda Undocumented

Inherited from UsesInspection (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole, FromClauseRole, JoinTargetRole):

Class Variable	`_post_inspect`	Undocumented
Class Variable	`uses_inspection`	Undocumented

Inherited from SQLRole (via AliasedReturnsRows, FromClause, AnonymizedFromClauseRole, StrictFromClauseRole, FromClauseRole, JoinTargetRole, StructuralRole):

Class Variable	`allows_lambda`	Undocumented
Class Variable	`uses_inspection`	Undocumented

Inherited from Selectable (via AliasedReturnsRows, FromClause):

Method	`corresponding_column`	No summary
Method	`lateral`	Return a LATERAL alias of this `_expression.Selectable`.
Method	`replace_selectable`	Replace all occurrences of `_expression.FromClause` 'old' with the given `_expression.Alias` object, returning a copy of this `_expression.FromClause`.

Inherited from ReturnsRows (via AliasedReturnsRows, FromClause, Selectable):

Class Variable	`_is_lateral`	Undocumented
Class Variable	`_is_returns_rows`	Undocumented
Class Variable	`_is_select_statement`	Undocumented
Property	`_all_selected_columns`	A sequence of column expression objects that represents the "selected" columns of this `_expression.ReturnsRows`.
Property	`selectable`	Undocumented

Inherited from ReturnsRowsRole (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows):

Class Variable _role_name Undocumented

Inherited from SQLRole (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ReturnsRowsRole):

Class Variable	`allows_lambda`	Undocumented
Class Variable	`uses_inspection`	Undocumented

Inherited from ClauseElement (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows):

Method	`compare`	Compare this `_expression.ClauseElement` to the given `_expression.ClauseElement`.
Method	`compile`	Compile this SQL expression.
Method	`params`	Return a copy with `_expression.bindparam` elements replaced.
Method	`self_group`	Apply a 'grouping' to this `_expression.ClauseElement`.
Method	`unique_params`	Return a copy with `_expression.bindparam` elements replaced.
Method	`__bool__`	Undocumented
Method	`__getstate__`	Undocumented
Method	`__invert__`	Undocumented
Method	`__repr__`	Undocumented
Method	`__str__`	Undocumented
Method	`_clone`	Create a shallow copy of this ClauseElement.
Method	`_cloned_set`	Return the set consisting all cloned ancestors of this ClauseElement.
Method	`_compile_w_cache`	Undocumented
Method	`_compiler`	Return a compiler appropriate for this ClauseElement, given a Dialect.
Method	`_execute_on_connection`	Undocumented
Method	`_negate`	Undocumented
Method	`_negate_in_binary`	a hook to allow the right side of a binary expression to respond to a negation of the binary expression.
Method	`_replace_params`	Undocumented
Method	`_set_propagate_attrs`	Undocumented
Method	`_ungroup`	Return this `_expression.ClauseElement` without any groupings.
Method	`_with_binary_element_type`	in the context of binary expression, convert the type of this object to the one given.
Class Variable	`_cache_key_traversal`	Undocumented
Class Variable	`_is_bind_parameter`	Undocumented
Class Variable	`_is_clause_list`	Undocumented
Class Variable	`_is_clone_of`	Undocumented
Class Variable	`_is_immutable`	Undocumented
Class Variable	`_is_lambda_element`	Undocumented
Class Variable	`_is_select_container`	Undocumented
Class Variable	`_is_singleton_constant`	Undocumented
Class Variable	`_is_text_clause`	Undocumented
Class Variable	`_is_textual`	Undocumented
Class Variable	`_order_by_label_element`	Undocumented
Class Variable	`is_clause_element`	Undocumented
Class Variable	`stringify_dialect`	Undocumented
Class Variable	`supports_execution`	Undocumented
Instance Variable	`_propagate_attrs`	like annotations, however these propagate outwards liberally as SQL constructs are built, and are set up at construction time.
Property	`_constructor`	return the 'constructor' for this ClauseElement.

Inherited from SQLRole (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ClauseElement):

Class Variable	`allows_lambda`	Undocumented
Class Variable	`uses_inspection`	Undocumented

Inherited from SupportsWrappingAnnotations (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ClauseElement):

Method	`_annotate`	return a copy of this ClauseElement with annotations updated by the given dictionary.
Method	`_deannotate`	return a copy of this `_expression.ClauseElement` with annotations removed.
Method	`_with_annotations`	return a copy of this ClauseElement with annotations replaced by the given dictionary.

Inherited from SupportsAnnotations (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ClauseElement, SupportsWrappingAnnotations):

Property _annotations_cache_key Undocumented

Inherited from MemoizedHasCacheKey (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ClauseElement):

Method _generate_cache_key return a cache key.

Inherited from HasCacheKey (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ClauseElement, MemoizedHasCacheKey):

Class Variable	`inherit_cache`	Indicate if this `.HasCacheKey` instance should make use of the cache key generation scheme used by its immediate superclass.
Class Method	`_generate_cache_attrs`	generate cache key dispatcher for a new class.
Class Method	`_generate_cache_key_for_object`	Undocumented
Method	`_gen_cache_key`	return an optional cache key.
Class Variable	`__slots__`	Undocumented
Class Variable	`_hierarchy_supports_caching`	private attribute which may be set to False to prevent the inherit_cache warning from being emitted for a hierarchy of subclasses.
Class Variable	`_is_has_cache_key`	Undocumented

Inherited from Traversible (via AliasedReturnsRows, FromClause, Selectable, ReturnsRows, ClauseElement):

Method	`get_children`	Return immediate child `.visitors.Traversible` elements of this `.visitors.Traversible`.
Method	`__class_getitem__`	Undocumented

@classmethod
def _factory(cls, selectable, sampling, name=None, seed=None):

overrides sqlalchemy.sql.expression.AliasedReturnsRows._factory

Return a _expression.TableSample object.

_expression.TableSample is an _expression.Alias subclass that represents a table with the TABLESAMPLE clause applied to it. _expression.tablesample is also available from the _expression.FromClause class via the _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())

New in version 1.1.

Parameters
selectable	Undocumented
sampling	a `float` percentage between 0 and 100 or `_functions.Function`.
name	optional alias name
seed	any real-valued SQL expression. When specified, the REPEATABLE sub-clause is also rendered.

def _get_method(self):

Undocumented

@util.preload_module('sqlalchemy.sql.functions')
def _init(self, selectable, sampling, name=None, seed=None):

overrides sqlalchemy.sql.expression.AliasedReturnsRows._init

Undocumented

__visit_name__: str =

overrides sqlalchemy.sql.expression.FromClause.__visit_name__

Undocumented

_traverse_internals =

overrides sqlalchemy.sql.expression.AliasedReturnsRows._traverse_internals

Undocumented

sampling =

Undocumented

seed =

Undocumented