django orm queryset - 如何执行 sql 查询 MIN/MAX FILTER

Question

我正在尝试寻求帮助，为特定的 sql 语句创建 Django ORM 查询集（您也可以在此处运行它） https://dbfiddle.uk/?rdbms=postgres_13&fiddle=31c9431d6753e2fdd8df37bbc1869e88

特别是这个问题，我对包含以下内容的行更感兴趣：

MIN(created_at::time) FILTER (WHERE activity_type = 1) as min_time_in,
MAX(created_at::time) FILTER (WHERE activity_type = 2) as max_time_out

这里是整个 sql 如果可能转换为 django ORM 查询集

SELECT 
    created_at::date as created_date,
    company_id,
    employee_id,
    MIN(created_at::time) FILTER (WHERE activity_type = 1) as min_time_in,
    MAX(created_at::time) FILTER (WHERE activity_type = 2) as max_time_out
FROM
   timerecord
where date(created_at) = '2020-11-18' and employee_id = 1
GROUP BY created_date, company_id, employee_id
ORDER BY created_date, employee_id

Answer 1

原查询：

SELECT 
    created_at::date as created_date,
    company_id,
    employee_id,
    MIN(created_at::time) FILTER (WHERE activity_type = 1) as min_time_in,
    MAX(created_at::time) FILTER (WHERE activity_type = 2) as max_time_out
FROM
   timerecord
where date(created_at) = '2020-11-18' and employee_id = 1
GROUP BY created_date, company_id, employee_id
ORDER BY created_date, employee_id;

是conditional/selective aggregation的一个例子。上面的语法在 PostgreSQL/SQLite.

中可用

可以使用 CASE 表达式轻松重写为：

SELECT 
    created_at::date as created_date,
    company_id,
    employee_id,
    MIN(CASE WHEN activity_type = 1 THEN created_at::time END)as min_time_in,
    MAX(CASE WHEN activity_type = 2 THEN created_at::time END) as max_time_out
FROM
   timerecord
where date(created_at) = '2020-11-18' and employee_id = 1
GROUP BY created_date, company_id, employee_id
ORDER BY created_date, employee_id;

db<>fiddle demo

任何现代 RDBMS 都支持它，Django 也支持它：

conditional-aggregation

What if we want to find out how many clients there are for each account_type? We can nest conditional expression within aggregate functions to achieve this:
Client.objects.aggregate(
...     regular=Count('pk', filter=Q(account_type=Client.REGULAR)),
...     gold=Count('pk', filter=Q(account_type=Client.GOLD)),
...     platinum=Count('pk', filter=Q(account_type=Client.PLATINUM)),
... )
This aggregate produces a query with the SQL 2003 FILTER WHERE syntax on databases that support it

...

On other databases, this is emulated using a CASE statement

Answer 2

您可以将 aggregate()--(doc) method or (annotate()--(doc) method) to get the result. For that, you must use the Min() and Max() 数据库函数与 filter 参数一起使用。

from django.db.models import Min, Q, Max

agg_response = TimeRecord.objects.aggregate(
    <b>min_time_in=Min("created_at", filter=Q(activity_type=1)),
    max_time_out=Max("created_at", filter=Q(activity_type=2)),</b>
)

django orm queryset - 如何执行 sql 查询 MIN/MAX FILTER

django orm queryset - how to perform sql query MIN/MAX FILTER

sql

django

orm

max

filter