PostgreSQL specific aggregation functions¶
These functions are available from the django.contrib.postgres.aggregates
module. They are described in more detail in the PostgreSQL docs.
Note
All functions come without default aliases, so you must explicitly provide one. For example:
>>> SomeModel.objects.aggregate(arr=ArrayAgg('somefield'))
{'arr': [0, 1, 2]}
General-purpose aggregation functions¶
ArrayAgg
¶
-
class
ArrayAgg
(expression, distinct=False, filter=None, ordering=(), **extra)[source]¶ Returns a list of values, including nulls, concatenated into an array.
-
distinct
¶ An optional boolean argument that determines if array values will be distinct. Defaults to
False
.
-
ordering
¶ An optional string of a field name (with an optional
"-"
prefix which indicates descending order) or an expression (or a tuple or list of strings and/or expressions) that specifies the ordering of the elements in the result list.Examples:
'some_field' '-some_field' from django.db.models import F F('some_field').desc()
-
BitAnd
¶
BitOr
¶
BoolAnd
¶
-
class
BoolAnd
(expression, filter=None, **extra)[source]¶ Returns
True
, if all input values are true,None
if all values are null or if there are no values, otherwiseFalse
.Usage example:
class Comment(models.Model): body = models.TextField() published = models.BooleanField() rank = models.IntegerField() >>> from django.db.models import Q >>> from django.contrib.postgres.aggregates import BoolAnd >>> Comment.objects.aggregate(booland=BoolAnd('published')) {'booland': False} >>> Comment.objects.aggregate(booland=BoolAnd(Q(rank__lt=100))) {'booland': True}
BoolOr
¶
-
class
BoolOr
(expression, filter=None, **extra)[source]¶ Returns
True
if at least one input value is true,None
if all values are null or if there are no values, otherwiseFalse
.Usage example:
class Comment(models.Model): body = models.TextField() published = models.BooleanField() rank = models.IntegerField() >>> from django.db.models import Q >>> from django.contrib.postgres.aggregates import BoolOr >>> Comment.objects.aggregate(boolor=BoolOr('published')) {'boolor': True} >>> Comment.objects.aggregate(boolor=BoolOr(Q(rank__gt=2))) {'boolor': False}
JSONBAgg
¶
-
class
JSONBAgg
(expressions, distinct=False, filter=None, ordering=(), **extra)[source]¶ Returns the input values as a
JSON
array.-
distinct
¶ - New in Django 3.2.
An optional boolean argument that determines if array values will be distinct. Defaults to
False
.
-
ordering
¶ - New in Django 3.2.
An optional string of a field name (with an optional
"-"
prefix which indicates descending order) or an expression (or a tuple or list of strings and/or expressions) that specifies the ordering of the elements in the result list.Examples are the same as for
ArrayAgg.ordering
.
-
StringAgg
¶
-
class
StringAgg
(expression, delimiter, distinct=False, filter=None, ordering=())[source]¶ Returns the input values concatenated into a string, separated by the
delimiter
string.-
delimiter
¶ Required argument. Needs to be a string.
-
distinct
¶ An optional boolean argument that determines if concatenated values will be distinct. Defaults to
False
.
-
ordering
¶ An optional string of a field name (with an optional
"-"
prefix which indicates descending order) or an expression (or a tuple or list of strings and/or expressions) that specifies the ordering of the elements in the result string.Examples are the same as for
ArrayAgg.ordering
.
-
Aggregate functions for statistics¶
y
and x
¶
The arguments y
and x
for all these functions can be the name of a
field or an expression returning a numeric data. Both are required.
Corr
¶
CovarPop
¶
-
class
CovarPop
(y, x, sample=False, filter=None)[source]¶ Returns the population covariance as a
float
, orNone
if there aren’t any matching rows.Has one optional argument:
-
sample
¶ By default
CovarPop
returns the general population covariance. However, ifsample=True
, the return value will be the sample population covariance.
-
RegrAvgX
¶
RegrAvgY
¶
RegrCount
¶
RegrIntercept
¶
RegrR2
¶
RegrSlope
¶
RegrSXX
¶
RegrSXY
¶
Usage examples¶
We will use this example table:
| FIELD1 | FIELD2 | FIELD3 |
|--------|--------|--------|
| foo | 1 | 13 |
| bar | 2 | (null) |
| test | 3 | 13 |
Here’s some examples of some of the general-purpose aggregation functions:
>>> TestModel.objects.aggregate(result=StringAgg('field1', delimiter=';'))
{'result': 'foo;bar;test'}
>>> TestModel.objects.aggregate(result=ArrayAgg('field2'))
{'result': [1, 2, 3]}
>>> TestModel.objects.aggregate(result=ArrayAgg('field1'))
{'result': ['foo', 'bar', 'test']}
The next example shows the usage of statistical aggregate functions. The underlying math will be not described (you can read about this, for example, at wikipedia):
>>> TestModel.objects.aggregate(count=RegrCount(y='field3', x='field2'))
{'count': 2}
>>> TestModel.objects.aggregate(avgx=RegrAvgX(y='field3', x='field2'),
... avgy=RegrAvgY(y='field3', x='field2'))
{'avgx': 2, 'avgy': 13}