SQL and Generic Functions — SQLAlchemy 1.1 Documentation

Release: 1.1.18 | Release Date: March 6, 2018

# SQLAlchemy 1.1 Documentation

# SQL and Generic Functions

SQL functions which are known to SQLAlchemy with regards to database-specific rendering, return types and argument behavior. Generic functions are invoked like all SQL functions, using the `func` attribute:

    select([func.count()]).select_from(sometable)

Note that any name not known to `func` generates the function name as is - there is no restriction on what SQL functions can be called, known or unknown to SQLAlchemy, built-in or user defined. The section here only describes those functions where SQLAlchemy already knows what argument and return types are in use.

SQL function API, factories, and built-in functions.

class `sqlalchemy.sql.functions.` `AnsiFunction`(**kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  `identifier` = 'AnsiFunction'
  `name` = 'AnsiFunction'

class `sqlalchemy.sql.functions.` `Function`(name, *clauses, **kw)

  Bases: `sqlalchemy.sql.functions.FunctionElement`

  Describe a named SQL function.

  See the superclass `FunctionElement` for a description of public methods.

  See also

  `func` - namespace which produces registered or ad-hoc `Function` instances.

  `GenericFunction` - allows creation of registered function types.

  `__init__`(name, *clauses, **kw)

    Construct a `Function`.

    The `func` construct is normally used to construct new `Function` instances.

class `sqlalchemy.sql.functions.` `FunctionElement`(*clauses, **kwargs)

  Bases: `sqlalchemy.sql.expression.Executable`, `sqlalchemy.sql.expression.ColumnElement`, `sqlalchemy.sql.expression.FromClause`

  Base for SQL function-oriented constructs.

  See also

  `Function` - named SQL function.

  `func` - namespace which produces registered or ad-hoc `Function` instances.

  `GenericFunction` - allows creation of registered function types.

  `__init__`(*clauses, **kwargs)

    Construct a `FunctionElement`.

  `alias`(name=None, flat=False)

    Produce a `Alias` construct against this `FunctionElement`.

    This construct wraps the function in a named alias which is suitable for the FROM clause, in the style accepted for example by PostgreSQL.

    e.g.:

        from sqlalchemy.sql import column

        stmt = select([column('data_view')]).\
            select_from(SomeTable).\
            select_from(func.unnest(SomeTable.data).alias('data_view')
        )

    Would produce:

        SELECT data_view
        FROM sometable, unnest(sometable.data) AS data_view

    New in version 0.9.8: The `FunctionElement.alias()` method is now supported. Previously, this method’s behavior was undefined and did not behave consistently across versions.

  `clauses`

    Return the underlying `ClauseList` which contains the arguments for this `FunctionElement`.

  `columns`

    The set of columns exported by this `FunctionElement`.

    Function objects currently have no result column names built in; this method returns a single-element column collection with an anonymously named column.

    An interim approach to providing named columns for a function as a FROM clause is to build a `select()` with the desired columns:

        from sqlalchemy.sql import column

        stmt = select([column('x'), column('y')]).                select_from(func.myfunction())

  `execute`()

    Execute this `FunctionElement` against an embedded ‘bind’.

    This first calls `select()` to produce a SELECT construct.

    Note that `FunctionElement` can be passed to the `Connectable.execute()` method of `Connection` or `Engine`.

  `filter`(*criterion)

    Produce a FILTER clause against this function.

    Used against aggregate and window functions, for database backends that support the “FILTER” clause.

    The expression:

        func.count(1).filter(True)

    is shorthand for:

        from sqlalchemy import funcfilter
        funcfilter(func.count(1), True)

    New in version 1.0.0.

    See also

    `FunctionFilter`

    `funcfilter()`

  `get_children`(**kwargs)

    Return immediate child elements of this `ClauseElement`.

    This is used for visit traversal.

    **kwargs may contain flags that change the collection that is returned, for example to return a subset of items in order to cut down on larger traversals, or to return child items from a different context (such as schema-level collections instead of clause-level).

  `over`(partition_by=None, order_by=None, rows=None, range_=None)

    Produce an OVER clause against this function.

    Used against aggregate or so-called “window” functions, for database backends that support window functions.

    The expression:

        func.row_number().over(order_by='x')

    is shorthand for:

        from sqlalchemy import over
        over(func.row_number(), order_by='x')

    See `over()` for a full description.

    New in version 0.7.

  `packagenames` = ()
  `scalar`()

    Execute this `FunctionElement` against an embedded ‘bind’ and return a scalar value.

    This first calls `select()` to produce a SELECT construct.

    Note that `FunctionElement` can be passed to the `Connectable.scalar()` method of `Connection` or `Engine`.

  `select`()

    Produce a `select()` construct against this `FunctionElement`.

    This is shorthand for:

        s = select([function_element])

  `self_group`(against=None)

    Apply a ‘grouping’ to this `ClauseElement`.

    This method is overridden by subclasses to return a “grouping” construct, i.e. parenthesis. In particular it’s used by “binary” expressions to provide a grouping around themselves when placed into a larger expression, as well as by `select()` constructs when placed into the FROM clause of another `select()`. (Note that subqueries should be normally created using the `Select.alias()` method, as many platforms require nested SELECT statements to be named).

    As expressions are composed together, the application of `self_group()` is automatic - end-user code should never need to use this method directly. Note that SQLAlchemy’s clause constructs take operator precedence into account - so parenthesis might not be needed, for example, in an expression like `x OR (y AND z)` - AND takes precedence over OR.

    The base `self_group()` method of `ClauseElement` just returns self.

  `within_group`(*order_by)

    Produce a WITHIN GROUP (ORDER BY expr) clause against this function.

    Used against so-called “ordered set aggregate” and “hypothetical set aggregate” functions, including `percentile_cont`, `rank`, `dense_rank`, etc.

    See `within_group()` for a full description.

    New in version 1.1.

  `within_group_type`(within_group)

    For types that define their return type as based on the criteria within a WITHIN GROUP (ORDER BY) expression, called by the `WithinGroup` construct.

    Returns None by default, in which case the function’s normal `.type` is used.

class `sqlalchemy.sql.functions.` `GenericFunction`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.Function`

  Define a ‘generic’ function.

  A generic function is a pre-established `Function` class that is instantiated automatically when called by name from the `func` attribute. Note that calling any name from `func` has the effect that a new `Function` instance is created automatically, given that name. The primary use case for defining a `GenericFunction` class is so that a function of a particular name may be given a fixed return type. It can also include custom argument parsing schemes as well as additional methods.

  Subclasses of `GenericFunction` are automatically registered under the name of the class. For example, a user-defined function `as_utc()` would be available immediately:

      from sqlalchemy.sql.functions import GenericFunction
      from sqlalchemy.types import DateTime

      class as_utc(GenericFunction):
          type = DateTime

      print select([func.as_utc()])

  User-defined generic functions can be organized into packages by specifying the “package” attribute when defining `GenericFunction`. Third party libraries containing many functions may want to use this in order to avoid name conflicts with other systems. For example, if our `as_utc()` function were part of a package “time”:

      class as_utc(GenericFunction):
          type = DateTime
          package = "time"

  The above function would be available from `func` using the package name `time`:

      print select([func.time.as_utc()])

  A final option is to allow the function to be accessed from one name in `func` but to render as a different name. The `identifier` attribute will override the name used to access the function as loaded from `func`, but will retain the usage of `name` as the rendered name:

      class GeoBuffer(GenericFunction):
          type = Geometry
          package = "geo"
          name = "ST_Buffer"
          identifier = "buffer"

  The above function will render as follows:

      >>> print func.geo.buffer()
      ST_Buffer()

  New in version 0.8: `GenericFunction` now supports automatic registration of new functions as well as package and custom naming support.

  Changed in version 0.8: The attribute name `type` is used to specify the function’s return type at the class level. Previously, the name `__return_type__` was used. This name is still recognized for backwards-compatibility.

  `coerce_arguments` = True
  `identifier` = 'GenericFunction'
  `name` = 'GenericFunction'

class `sqlalchemy.sql.functions.` `OrderedSetAgg`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Define a function where the return type is based on the sort expression type as defined by the expression passed to the `FunctionElement.within_group()` method.

  `array_for_multi_clause` = False
  `identifier` = 'OrderedSetAgg'
  `name` = 'OrderedSetAgg'
  `within_group_type`(within_group)

    For types that define their return type as based on the criteria within a WITHIN GROUP (ORDER BY) expression, called by the `WithinGroup` construct.

    Returns None by default, in which case the function’s normal `.type` is used.

class `sqlalchemy.sql.functions.` `ReturnTypeFromArgs`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Define a function whose return type is the same as its arguments.

  `identifier` = 'ReturnTypeFromArgs'
  `name` = 'ReturnTypeFromArgs'

class `sqlalchemy.sql.functions.` `array_agg`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  support for the ARRAY_AGG function.

  The `func.array_agg(expr)` construct returns an expression of type `types.ARRAY`.

  e.g.:

      stmt = select([func.array_agg(table.c.values)[2:5]])

  New in version 1.1.

  See also

  `postgresql.array_agg()` - PostgreSQL-specific version that returns `postgresql.ARRAY`, which has PG-specific operators added.

  `identifier` = 'array_agg'
  `name` = 'array_agg'
  `type`

    alias of `sqlalchemy.sql.sqltypes.ARRAY`

class `sqlalchemy.sql.functions.` `char_length`(arg, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  `identifier` = 'char_length'
  `name` = 'char_length'
  `type`

    alias of `sqlalchemy.sql.sqltypes.Integer`

class `sqlalchemy.sql.functions.` `coalesce`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.ReturnTypeFromArgs`

  `identifier` = 'coalesce'
  `name` = 'coalesce'

class `sqlalchemy.sql.functions.` `concat`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  `identifier` = 'concat'
  `name` = 'concat'
  `type`

    alias of `sqlalchemy.sql.sqltypes.String`

class `sqlalchemy.sql.functions.` `count`(expression=None, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  The ANSI COUNT aggregate function. With no arguments, emits COUNT *.

  `identifier` = 'count'
  `name` = 'count'
  `type`

    alias of `sqlalchemy.sql.sqltypes.Integer`

class `sqlalchemy.sql.functions.` `cume_dist`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Implement the `cume_dist` hypothetical-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is `Numeric`.

  New in version 1.1.

  `identifier` = 'cume_dist'
  `name` = 'cume_dist'
  `type` = Numeric()

class `sqlalchemy.sql.functions.` `current_date`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'current_date'
  `name` = 'current_date'
  `type`

    alias of `sqlalchemy.sql.sqltypes.Date`

class `sqlalchemy.sql.functions.` `current_time`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'current_time'
  `name` = 'current_time'
  `type`

    alias of `sqlalchemy.sql.sqltypes.Time`

class `sqlalchemy.sql.functions.` `current_timestamp`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'current_timestamp'
  `name` = 'current_timestamp'
  `type`

    alias of `sqlalchemy.sql.sqltypes.DateTime`

class `sqlalchemy.sql.functions.` `current_user`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'current_user'
  `name` = 'current_user'
  `type`

    alias of `sqlalchemy.sql.sqltypes.String`

class `sqlalchemy.sql.functions.` `dense_rank`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Implement the `dense_rank` hypothetical-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is `Integer`.

  New in version 1.1.

  `identifier` = 'dense_rank'
  `name` = 'dense_rank'
  `type` = Integer()

class `sqlalchemy.sql.functions.` `localtime`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'localtime'
  `name` = 'localtime'
  `type`

    alias of `sqlalchemy.sql.sqltypes.DateTime`

class `sqlalchemy.sql.functions.` `localtimestamp`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'localtimestamp'
  `name` = 'localtimestamp'
  `type`

    alias of `sqlalchemy.sql.sqltypes.DateTime`

class `sqlalchemy.sql.functions.` `max`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.ReturnTypeFromArgs`

  `identifier` = 'max'
  `name` = 'max'

class `sqlalchemy.sql.functions.` `min`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.ReturnTypeFromArgs`

  `identifier` = 'min'
  `name` = 'min'

class `sqlalchemy.sql.functions.` `mode`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.OrderedSetAgg`

  implement the `mode` ordered-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is the same as the sort expression.

  New in version 1.1.

  `identifier` = 'mode'
  `name` = 'mode'

class `sqlalchemy.sql.functions.` `next_value`(seq, **kw)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Represent the ‘next value’, given a `Sequence` as its single argument.

  Compiles into the appropriate function on each backend, or will raise NotImplementedError if used on a backend that does not provide support for sequences.

  `identifier` = 'next_value'
  `name` = 'next_value'
  `type` = Integer()

class `sqlalchemy.sql.functions.` `now`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  `identifier` = 'now'
  `name` = 'now'
  `type`

    alias of `sqlalchemy.sql.sqltypes.DateTime`

class `sqlalchemy.sql.functions.` `percent_rank`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Implement the `percent_rank` hypothetical-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is `Numeric`.

  New in version 1.1.

  `identifier` = 'percent_rank'
  `name` = 'percent_rank'
  `type` = Numeric()

class `sqlalchemy.sql.functions.` `percentile_cont`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.OrderedSetAgg`

  implement the `percentile_cont` ordered-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is the same as the sort expression, or if the arguments are an array, an `types.ARRAY` of the sort expression’s type.

  New in version 1.1.

  `array_for_multi_clause` = True
  `identifier` = 'percentile_cont'
  `name` = 'percentile_cont'

class `sqlalchemy.sql.functions.` `percentile_disc`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.OrderedSetAgg`

  implement the `percentile_disc` ordered-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is the same as the sort expression, or if the arguments are an array, an `types.ARRAY` of the sort expression’s type.

  New in version 1.1.

  `array_for_multi_clause` = True
  `identifier` = 'percentile_disc'
  `name` = 'percentile_disc'

class `sqlalchemy.sql.functions.` `random`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  `identifier` = 'random'
  `name` = 'random'

class `sqlalchemy.sql.functions.` `rank`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.GenericFunction`

  Implement the `rank` hypothetical-set aggregate function.

  This function must be used with the `FunctionElement.within_group()` modifier to supply a sort expression to operate upon.

  The return type of this function is `Integer`.

  New in version 1.1.

  `identifier` = 'rank'
  `name` = 'rank'
  `type` = Integer()

`sqlalchemy.sql.functions.` `register_function`(identifier, fn, package='_default')

  Associate a callable with a particular func. name.

  This is normally called by _GenericMeta, but is also available by itself so that a non-Function construct can be associated with the `func` accessor (i.e. CAST, EXTRACT).

class `sqlalchemy.sql.functions.` `session_user`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'session_user'
  `name` = 'session_user'
  `type`

    alias of `sqlalchemy.sql.sqltypes.String`

class `sqlalchemy.sql.functions.` `sum`(*args, **kwargs)

  Bases: `sqlalchemy.sql.functions.ReturnTypeFromArgs`

  `identifier` = 'sum'
  `name` = 'sum'

class `sqlalchemy.sql.functions.` `sysdate`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'sysdate'
  `name` = 'sysdate'
  `type`

    alias of `sqlalchemy.sql.sqltypes.DateTime`

class `sqlalchemy.sql.functions.` `user`(**kwargs)

  Bases: `sqlalchemy.sql.functions.AnsiFunction`

  `identifier` = 'user'
  `name` = 'user'
  `type`

    alias of `sqlalchemy.sql.sqltypes.String`