Count

The count query makes it really easy to retrieve the number of rows in a table:

>>> await Band.count()
3

It’s equivalent to this select query:

from piccolo.query.methods.select import Count

>>> response = await Band.select(Count())
>>> response[0]['count']
3

As you can see, the count query is more convenient.

Non-null columns

If you want to retrieve the number of rows where a given column isn’t null, we can do so as follows:

await Band.count(column=Band.name)

# Or simply:
await Band.count(Band.name)

Note, this is equivalent to:

await Band.count().where(Band.name.is_not_null())

Example

If we have the following database table:

class Band(Table):
    name = Varchar()
    popularity = Integer(null=True)

With the following data:

name	popularity
Pythonistas	1000
Rustaceans	800
C-Sharps	null

Then we get the following results:

>>> await Band.count()
3

>>> await Band.count(Band.popularity)
2

distinct

We can count the number of distinct (i.e. unique) rows.

await Band.count(distinct=[Band.name])

# This also works - use whichever you prefer:
await Band.count().distinct([Band.name])

With the following data:

name	popularity
Pythonistas	1000
Pythonistas	1000
Pythonistas	800
Rustaceans	800

Note how we have duplicate band names.

Hint

This is bad database design as we should add a unique constraint to prevent this, but go with it for this example!

Let’s compare queries with and without distinct:

>>> await Band.count()
4

>>> await Band.count(distinct=[Band.name])
2

We can specify multiple columns:

>>> await Band.count(distinct=[Band.name, Band.popularity])
3

In the above example, this means we count rows where the combination of name and popularity is unique.

So ('Pythonistas', 1000) is a distinct value from ('Pythonistas', 800), because even though the name is the same, the popularity is different.

Clauses

where

See where.