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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.

General-purpose aggregation functions

ArrayAgg

class ArrayAgg(expression, distinct=False, filter=None, ordering=(), **extra)

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.

Exemplos:

Code
'some_field'
'-some_field'
from django.db.models import F
F('some_field').desc()

BitAnd

class BitAnd(expression, filter=None, **extra)

Returns an int of the bitwise AND of all non-null input values, or None if all values are null.

BitOr

class BitOr(expression, filter=None, **extra)

Returns an int of the bitwise OR of all non-null input values, or None if all values are null.

BoolAnd

class BoolAnd(expression, filter=None, **extra)

Returns True, if all input values are true, None if all values are null or if there are no values, otherwise False .

BoolOr

class BoolOr(expression, filter=None, **extra)

Returns True if at least one input value is true, None if all values are null or if there are no values, otherwise False.

JSONBAgg

class JSONBAgg(expressions, filter=None, **extra)

Returns the input values as a JSON array. Requires PostgreSQL ≥ 9.5.

StringAgg

class StringAgg(expression, delimiter, distinct=False, filter=None, ordering=())

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

class Corr(y, x, filter=None)

Returns the correlation coefficient as a float, or None if there aren’t any matching rows.

CovarPop

class CovarPop(y, x, sample=False, filter=None)

Returns the population covariance as a float, or None if there aren’t any matching rows.

Has one optional argument:

sample

By default CovarPop returns the general population covariance. However, if sample=True, the return value will be the sample population covariance.

RegrAvgX

class RegrAvgX(y, x, filter=None)

Returns the average of the independent variable (sum(x)/N) as a float, or None if there aren’t any matching rows.

RegrAvgY

class RegrAvgY(y, x, filter=None)

Returns the average of the dependent variable (sum(y)/N) as a float, or None if there aren’t any matching rows.

RegrCount

class RegrCount(y, x, filter=None)

Returns an int of the number of input rows in which both expressions are not null.

RegrIntercept

class RegrIntercept(y, x, filter=None)

Returns the y-intercept of the least-squares-fit linear equation determined by the (x, y) pairs as a float, or None if there aren’t any matching rows.

RegrR2

class RegrR2(y, x, filter=None)

Returns the square of the correlation coefficient as a float, or None if there aren’t any matching rows.

RegrSlope

class RegrSlope(y, x, filter=None)

Returns the slope of the least-squares-fit linear equation determined by the (x, y) pairs as a float, or None if there aren’t any matching rows.

RegrSXX

class RegrSXX(y, x, filter=None)

Returns sum(x^2) - sum(x)^2/N (“sum of squares” of the independent variable) as a float, or None if there aren’t any matching rows.

RegrSXY

class RegrSXY(y, x, filter=None)

Returns sum(x*y) - sum(x) * sum(y)/N (“sum of products” of independent times dependent variable) as a float, or None if there aren’t any matching rows.

RegrSYY

class RegrSYY(y, x, filter=None)

Returns sum(y^2) - sum(y)^2/N (“sum of squares” of the dependent variable) as a float, or None if there aren’t any matching rows.

Usage examples

We will use this example table:

Code
| FIELD1 | FIELD2 | FIELD3 |
|--------|--------|--------|
|    foo |      1 |     13 |
|    bar |      2 | (null) |
|   test |      3 |     13 |

Here’s some examples of some of the general-purpose aggregation functions:

Code
>>> 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):

Code
>>> 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}
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