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:

  1. 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.

See also

Working with SQL Functions - in the SQLAlchemy 1.4 / 2.0 Tutorial

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

Object NameDescription

AnsiFunction

Define a function in “ansi” format, which doesn’t render parenthesis.

array_agg

Support for the ARRAY_AGG function.

char_length

The CHAR_LENGTH() SQL function.

coalesce

concat

The SQL CONCAT() function, which concatenates strings.

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

The CURRENT_DATE() SQL function.

current_time

The CURRENT_TIME() SQL function.

current_timestamp

The CURRENT_TIMESTAMP() SQL function.

current_user

The CURRENT_USER() SQL function.

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

The localtime() SQL function.

localtimestamp

The localtimestamp() SQL function.

max

The SQL MAX() aggregate function.

min

The SQL MIN() aggregate function.

mode

Implement the mode ordered-set aggregate function.

next_value

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

now

The SQL now() datetime function.

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

The RANDOM() SQL function.

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.

ScalarFunctionColumn

session_user

The SESSION_USER() SQL function.

sum

The SQL SUM() aggregate function.

sysdate

The SYSDATE() SQL function.

user

The USER() SQL function.

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

Define a function in “ansi” format, which doesn’t render parenthesis.

Class signature

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

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.:

      1. func.mypackage.some_function(col1, col2)

See also

Working with SQL Functions - in the SQLAlchemy 1.4 / 2.0 Tutorial

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

GenericFunction - allows creation of registered function types.

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.

  • attribute sqlalchemy.sql.functions.Function.type = NullType()

    A TypeEngine object which refers to the SQL return type represented by this SQL function.

    This datatype may be configured when generating a Function object by passing the Function.type_ parameter, e.g.:

    1. >>> select(func.lower("some VALUE", type_=String))

    The small number of built-in classes of Function come with a built-in datatype that’s appropriate to the class of function and its arguments. For functions that aren’t known, the type defaults to the “null type”.

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

Class signature

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

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.

Class signature

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

  1. See also
  2. [`func`]($f62ce11674ae62ed.md#sqlalchemy.sql.expression.func "sqlalchemy.sql.expression.func")
  3. [`Function`](#sqlalchemy.sql.functions.Function "sqlalchemy.sql.functions.Function")
  • method sqlalchemy.sql.functions.FunctionElement.alias(name=None)

    Produce a Alias construct against this FunctionElement.

    Tip

    The FunctionElement.alias() method is part of the mechanism by which “table valued” SQL functions are created. However, most use cases are covered by higher level methods on FunctionElement including FunctionElement.table_valued(), and FunctionElement.column_valued().

    This construct wraps the function in a named alias which is suitable for the FROM clause, in the style accepted for example by PostgreSQL. A column expression is also provided using the special .column attribute, which may be used to refer to the output of the function as a scalar value in the columns or where clause, for a backend such as PostgreSQL.

    For a full table-valued expression, use the FunctionElement.table_valued() method first to establish named columns.

    e.g.:

    1. >>> from sqlalchemy import func, select, column
    2. >>> data_view = func.unnest([1, 2, 3]).alias("data_view")
    3. >>> print(select(data_view.column))
    4. SELECT data_view
    5. FROM unnest(:unnest_1) AS data_view

    The FunctionElement.column_valued() method provides a shortcut for the above pattern:

    1. >>> data_view = func.unnest([1, 2, 3]).column_valued("data_view")
    2. >>> print(select(data_view))
    3. SELECT data_view
    4. FROM unnest(:unnest_1) AS data_view

    New in version 1.4.0b2: Added the .column accessor

    See also

    Table-Valued Functions - in the SQLAlchemy 1.4 / 2.0 Tutorial

    FunctionElement.table_valued()

    FunctionElement.scalar_table_valued()

    FunctionElement.column_valued()

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

    Interpret this expression as a boolean comparison between two values.

    This method is used for an ORM use case described at Custom operators based on SQL functions.

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

    1. 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:

    1. 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:

    1. 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:

    1. class Venue(Base):
    2. __tablename__ = 'venue'
    3. id = Column(Integer, primary_key=True)
    4. name = Column(String)
    5. descendants = relationship(
    6. "Venue",
    7. primaryjoin=func.instr(
    8. remote(foreign(name)), name + "/"
    9. ).as_comparison(1, 2) == 1,
    10. viewonly=True,
    11. order_by=name
    12. )

    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.

  1. New in version 1.3.
  2. See also
  3. [Custom operators based on SQL functions]($e1f42b7742e49253.md#relationship-custom-operator-sql-function) - example use within the ORM
  1. New in version 1.4.0b2.
  2. See also
  3. [Table-Valued Functions]($cfdc81b69abe0678.md#tutorial-functions-table-valued) - in the [SQLAlchemy 1.4 / 2.0 Tutorial]($2006f9816d864d8d.md#unified-tutorial)
  4. [Table-Valued Functions]($d951abc5c7ad81e4.md#postgresql-table-valued) - in the [PostgreSQL]($d951abc5c7ad81e4.md) documentation
  5. [`FunctionElement.scalar_table_valued()`](#sqlalchemy.sql.functions.FunctionElement.scalar_table_valued "sqlalchemy.sql.functions.FunctionElement.scalar_table_valued") - variant of [`FunctionElement.table_valued()`](#sqlalchemy.sql.functions.FunctionElement.table_valued "sqlalchemy.sql.functions.FunctionElement.table_valued") which delivers the complete table valued expression as a scalar column expression
  6. [`FunctionElement.column_valued()`](#sqlalchemy.sql.functions.FunctionElement.column_valued "sqlalchemy.sql.functions.FunctionElement.column_valued")
  7. [`TableValuedAlias.render_derived()`]($fc2d211e9d1454ca.md#sqlalchemy.sql.expression.TableValuedAlias.render_derived "sqlalchemy.sql.expression.TableValuedAlias.render_derived") - renders the alias using a derived column clause, e.g. `AS name(col1, col2, ...)`

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:

  1. from sqlalchemy.sql.functions import GenericFunction
  2. from sqlalchemy.types import DateTime
  3. class as_utc(GenericFunction):
  4. type = DateTime
  5. 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”:

  1. class as_utc(GenericFunction):
  2. type = DateTime
  3. package = "time"

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

  1. 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:

  1. class GeoBuffer(GenericFunction):
  2. type = Geometry
  3. package = "geo"
  4. name = "ST_Buffer"
  5. identifier = "buffer"

The above function will render as follows:

  1. >>> print(func.geo.buffer())
  2. 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:

  1. from sqlalchemy.sql import quoted_name
  2. class GeoBuffer(GenericFunction):
  3. type = Geometry
  4. package = "geo"
  5. name = quoted_name("ST_Buffer", True)
  6. identifier = "buffer"

The above function will render as:

  1. >>> print(func.geo.buffer())
  2. "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.

Class signature

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

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.

Class signature

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

  • 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.

Class signature

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

class sqlalchemy.sql.functions.``ScalarFunctionColumn(fn, name, type_=None)

Class signature

class sqlalchemy.sql.functions.ScalarFunctionColumn (sqlalchemy.sql.expression.NamedColumn)

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.:

  1. 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.

Class signature

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

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

The CHAR_LENGTH() SQL function.

Class signature

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

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

Class signature

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

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

The SQL CONCAT() function, which concatenates strings.

E.g.:

  1. >>> print(select(func.concat('a', 'b')))
  2. SELECT concat(:concat_2, :concat_3) AS concat_1

String concatenation in SQLAlchemy is more commonly available using the Python + operator with string datatypes, which will render a backend-specific concatenation operator, such as

  1. >>> print(select(literal("a") + "b"))
  2. SELECT :param_1 || :param_2 AS anon_1

Class signature

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

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

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

E.g.:

  1. from sqlalchemy import func
  2. from sqlalchemy import select
  3. from sqlalchemy import table, column
  4. my_table = table('some_table', column('id'))
  5. stmt = select(func.count()).select_from(my_table)

Executing stmt would emit:

  1. SELECT count(*) AS count_1
  2. FROM some_table

Class signature

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

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

Implement the CUBE grouping operation.

This function is used as part of the GROUP BY of a statement, e.g. Select.group_by():

  1. stmt = select(
  2. func.sum(table.c.value), table.c.col_1, table.c.col_2
  3. ).group_by(func.cube(table.c.col_1, table.c.col_2))

New in version 1.2.

Class signature

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

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

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.

Class signature

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

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

The CURRENT_DATE() SQL function.

Class signature

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

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

The CURRENT_TIME() SQL function.

Class signature

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

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

The CURRENT_TIMESTAMP() SQL function.

Class signature

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

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

The CURRENT_USER() SQL function.

Class signature

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

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

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.

Class signature

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

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

Implement the GROUPING SETS grouping operation.

This function is used as part of the GROUP BY of a statement, e.g. Select.group_by():

  1. stmt = select(
  2. func.sum(table.c.value), table.c.col_1, table.c.col_2
  3. ).group_by(func.grouping_sets(table.c.col_1, table.c.col_2))

In order to group by multiple sets, use the tuple_() construct:

  1. from sqlalchemy import tuple_
  2. stmt = select(
  3. func.sum(table.c.value),
  4. table.c.col_1, table.c.col_2,
  5. table.c.col_3
  6. ).group_by(
  7. func.grouping_sets(
  8. tuple_(table.c.col_1, table.c.col_2),
  9. tuple_(table.c.value, table.c.col_3),
  10. )
  11. )

New in version 1.2.

Class signature

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

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

The localtime() SQL function.

Class signature

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

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

The localtimestamp() SQL function.

Class signature

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

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

The SQL MAX() aggregate function.

Class signature

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

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

The SQL MIN() aggregate function.

Class signature

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

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

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.

Class signature

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

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

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.

Class signature

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

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

The SQL now() datetime function.

SQLAlchemy dialects will usually render this particular function in a backend-specific way, such as rendering it as CURRENT_TIMESTAMP.

Class signature

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

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

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.

Class signature

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

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

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 ARRAY of the sort expression’s type.

New in version 1.1.

Class signature

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

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

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 ARRAY of the sort expression’s type.

New in version 1.1.

Class signature

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

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

The RANDOM() SQL function.

Class signature

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

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

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.

Class signature

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

function 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.``rollup(\args, **kwargs*)

Implement the ROLLUP grouping operation.

This function is used as part of the GROUP BY of a statement, e.g. Select.group_by():

  1. stmt = select(
  2. func.sum(table.c.value), table.c.col_1, table.c.col_2
  3. ).group_by(func.rollup(table.c.col_1, table.c.col_2))

New in version 1.2.

Class signature

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

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

The SESSION_USER() SQL function.

Class signature

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

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

The SQL SUM() aggregate function.

Class signature

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

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

The SYSDATE() SQL function.

Class signature

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

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

The USER() SQL function.

Class signature

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