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.

Object Name	Description
AnsiFunction
array_agg	Support for the ARRAY_AGG function.
char_length
coalesce
concat
count	The ANSI COUNT aggregate function. With no arguments, emits COUNT *.
cube	Implement the `CUBE` grouping operation.
cume_dist	Implement the `cume_dist` hypothetical-set aggregate function.
current_date
current_time
current_timestamp
current_user
dense_rank	Implement the `dense_rank` hypothetical-set aggregate function.
Function	Describe a named SQL function.
FunctionAsBinary
FunctionElement	Base for SQL function-oriented constructs.
GenericFunction	Define a ‘generic’ function.
grouping_sets	Implement the `GROUPING SETS` grouping operation.
localtime
localtimestamp
max
min
mode	Implement the `mode` ordered-set aggregate function.
next_value	Represent the ‘next value’, given a `Sequence` as its single argument.
now
OrderedSetAgg	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.
percent_rank	Implement the `percent_rank` hypothetical-set aggregate function.
percentile_cont	Implement the `percentile_cont` ordered-set aggregate function.
percentile_disc	Implement the `percentile_disc` ordered-set aggregate function.
random
rank	Implement the `rank` hypothetical-set aggregate function.
register_function(identifier, fn[, package])	Associate a callable with a particular func. name.
ReturnTypeFromArgs	Define a function whose return type is the same as its arguments.
rollup	Implement the `ROLLUP` grouping operation.
session_user
sum
sysdate
user

class sqlalchemy.sql.functions.AnsiFunction(*args, **kwargs)¶

Members

identifier, name

Class signature

class sqlalchemy.sql.functions.AnsiFunction (sqlalchemy.sql.functions.GenericFunction)

attribute sqlalchemy.sql.functions.AnsiFunction.identifier = 'AnsiFunction'¶

attribute sqlalchemy.sql.functions.AnsiFunction.name = 'AnsiFunction'¶

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

Describe a named SQL function.

The Function object is typically generated from the func generation object.

Parameters:

*clauses – list of column expressions that form the arguments of the SQL function call.
type_ – optional TypeEngine datatype object that will be used as the return value of the column expression generated by this function call.
packagenames –
a string which indicates package prefix names to be prepended to the function name when the SQL is generated. The func generator creates these when it is called using dotted format, e.g.:
```
func.mypackage.some_function(col1, col2)
```

See also

Functions

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

GenericFunction - allows creation of registered function types.

Members

__init__()

Class signature

class sqlalchemy.sql.functions.Function (sqlalchemy.sql.functions.FunctionElement)

method sqlalchemy.sql.functions.Function.__init__(name, *clauses, **kw)¶

Construct a Function.

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

class sqlalchemy.sql.functions.FunctionAsBinary(fn, left_index, right_index)¶

Members

left, right

Class signature

class sqlalchemy.sql.functions.FunctionAsBinary (sqlalchemy.sql.expression.BinaryExpression)

attribute sqlalchemy.sql.functions.FunctionAsBinary.left¶

attribute sqlalchemy.sql.functions.FunctionAsBinary.right¶

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

Base for SQL function-oriented constructs.

See also

Functions - in the Core tutorial

Function - named SQL function.

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

GenericFunction - allows creation of registered function types.

Members

__init__(), alias(), as_comparison(), clauses, columns, execute(), filter(), get_children(), over(), packagenames, scalar(), select(), self_group(), within_group(), within_group_type()

Class signature

class sqlalchemy.sql.functions.FunctionElement (sqlalchemy.sql.expression.Executable, sqlalchemy.sql.expression.ColumnElement, sqlalchemy.sql.expression.FromClause)

method sqlalchemy.sql.functions.FunctionElement.__init__(*clauses, **kwargs)¶

Construct a FunctionElement.

Parameters:

*clauses – list of column expressions that form the arguments of the SQL function call.
**kwargs – additional kwargs are typically consumed by subclasses.

See also

func

Function

method sqlalchemy.sql.functions.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.

method sqlalchemy.sql.functions.FunctionElement.as_comparison(left_index, right_index)¶

Interpret this expression as a boolean comparison between two values.

A hypothetical SQL function “is_equal()” which compares to values for equality would be written in the Core expression language as:

expr = func.is_equal("a", "b")

If “is_equal()” above is comparing “a” and “b” for equality, the FunctionElement.as_comparison() method would be invoked as:

expr = func.is_equal("a", "b").as_comparison(1, 2)

Where above, the integer value “1” refers to the first argument of the “is_equal()” function and the integer value “2” refers to the second.

This would create a BinaryExpression that is equivalent to:

BinaryExpression("a", "b", operator=op.eq)

However, at the SQL level it would still render as “is_equal(‘a’, ‘b’)”.

The ORM, when it loads a related object or collection, needs to be able to manipulate the “left” and “right” sides of the ON clause of a JOIN expression. The purpose of this method is to provide a SQL function construct that can also supply this information to the ORM, when used with the relationship.primaryjoin parameter. The return value is a containment object called FunctionAsBinary.

An ORM example is as follows:

class Venue(Base):
    __tablename__ = 'venue'
    id = Column(Integer, primary_key=True)
    name = Column(String)

    descendants = relationship(
        "Venue",
        primaryjoin=func.instr(
            remote(foreign(name)), name + "/"
        ).as_comparison(1, 2) == 1,
        viewonly=True,
        order_by=name
    )

Above, the “Venue” class can load descendant “Venue” objects by determining if the name of the parent Venue is contained within the start of the hypothetical descendant value’s name, e.g. “parent1” would match up to “parent1/child1”, but not to “parent2/child1”.

Possible use cases include the “materialized path” example given above, as well as making use of special SQL functions such as geometric functions to create join conditions.

Parameters:

left_index – the integer 1-based index of the function argument that serves as the “left” side of the expression.
right_index – the integer 1-based index of the function argument that serves as the “right” side of the expression.

New in version 1.3.

attribute sqlalchemy.sql.functions.FunctionElement.clauses¶: Return the underlying ClauseList which contains the arguments for this FunctionElement.

attribute sqlalchemy.sql.functions.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())

method sqlalchemy.sql.functions.FunctionElement.execute()¶

Execute this FunctionElement against an embedded ‘bind’.

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

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

method sqlalchemy.sql.functions.FunctionElement.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()

method sqlalchemy.sql.functions.FunctionElement.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).

method sqlalchemy.sql.functions.FunctionElement.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.

attribute sqlalchemy.sql.functions.FunctionElement.packagenames = ()¶

method sqlalchemy.sql.functions.FunctionElement.scalar()¶

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

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

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

method sqlalchemy.sql.functions.FunctionElement.select()¶

Produce a select() construct against this FunctionElement.

This is shorthand for:

s = select([function_element])

method sqlalchemy.sql.functions.FunctionElement.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.

method sqlalchemy.sql.functions.FunctionElement.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.

method sqlalchemy.sql.functions.FunctionElement.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)¶

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()

The name will be rendered as is, however without quoting unless the name contains special characters that require quoting. To force quoting on or off for the name, use the quoted_name construct:

from sqlalchemy.sql import quoted_name

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

The above function will render as:

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

New in version 1.3.13: The quoted_name construct is now recognized for quoting when used with the “name” attribute of the object, so that quoting can be forced on or off for the function name.

Members

coerce_arguments, identifier, name

Class signature

class sqlalchemy.sql.functions.GenericFunction (sqlalchemy.sql.functions.Function)

attribute sqlalchemy.sql.functions.GenericFunction.coerce_arguments = True¶

attribute sqlalchemy.sql.functions.GenericFunction.identifier = 'GenericFunction'¶

attribute sqlalchemy.sql.functions.GenericFunction.name = 'GenericFunction'¶

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

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.

Members

array_for_multi_clause, identifier, name, within_group_type()

Class signature

class sqlalchemy.sql.functions.OrderedSetAgg (sqlalchemy.sql.functions.GenericFunction)

attribute sqlalchemy.sql.functions.OrderedSetAgg.array_for_multi_clause = False¶

attribute sqlalchemy.sql.functions.OrderedSetAgg.identifier = 'OrderedSetAgg'¶

attribute sqlalchemy.sql.functions.OrderedSetAgg.name = 'OrderedSetAgg'¶

method sqlalchemy.sql.functions.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)¶

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

Members

identifier, name

Class signature

class sqlalchemy.sql.functions.ReturnTypeFromArgs (sqlalchemy.sql.functions.GenericFunction)

attribute sqlalchemy.sql.functions.ReturnTypeFromArgs.identifier = 'ReturnTypeFromArgs'¶

attribute sqlalchemy.sql.functions.ReturnTypeFromArgs.name = 'ReturnTypeFromArgs'¶

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

Support for the ARRAY_AGG function.

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

e.g.:

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

New in version 1.1.

See also

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

Members

SQLAlchemy 1.3 Documentation

SQLAlchemy 1.3 Documentation

SQLAlchemy Core

SQL and Generic Functions¶