Django query count only on a specific column

Question

Why does Django's count() result in a SQL query like

SELECT COUNT(*)

and is there a way to just count on a single column?

For instance, having a model with the following rows: - id - first_name - last_name Instead of having the count run on * which is similar to SELECT COUNT(id, first_name, last_name) I would like to only run

SELECT COUNT(id)

Or best to do SELECT COUNT(1). I want to do this because I once heard that this would be faster for huge tables.

NOTE: If it's faster or not is not the question, it's how to do the query with Django. So please don't mark it as duplicated with Count(*) vs Count(1) - SQL Server

what do you mean "count on a single row"? What exactly do you want to count? Please be specific. — dirkgroten
– dirkgroten, Commented Sep 3, 2019 at 10:19
@dirkgroten I updated the question. Hope that makes it clearer. — ezdazuzena
– ezdazuzena, Commented Sep 3, 2019 at 10:36
stackoverflow.com/questions/1221559/count-vs-count1-sql-server — dirkgroten
– dirkgroten, Commented Sep 3, 2019 at 10:37
Note also that if you do COUNT(id) on column that may contain NULL values, you will receive a different result, as row with null values will not be counted. Use Django's aggregate if you actually want that. — dirkgroten
– dirkgroten, Commented Sep 3, 2019 at 10:42

dirkgroten · Accepted Answer · 2019-09-03 10:46:23Z

1

If the purpose is to count rows that do not have a NULL value in column x, you should use Django's aggregate:

MyModel.objects.aggregate(Count('x'))

But if your purpose is to speed up your query, than this is pointless as SELECT COUNT(*) or SELECT COUNT(x) have the exact same speed as explained here.

answered Sep 3, 2019 at 10:46

dirkgroten

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ezdazuzena · Accepted Answer · 2019-09-03 15:15:18Z

1

Try this

Entry.objects.values_list('field_name', flat=True).count()

edited Sep 3, 2019 at 15:15

ezdazuzena

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answered Sep 3, 2019 at 10:54

Asad

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