Django génère des requêtes différentes pour exclure avec Q et recherche de filtre simple - Stack Overflow

There is a simplified scheme of my models:

class A(Model):
   name = CharField()

class B(Model):
   a = models.ForeignKey(A, related_name='b', editable=False, null=False)
   valid = models.NullBooleanField(default=None)

So django generates two different queries for following statements:

1) Exclude with Q object

A.objects.filter().exclude(Q(b__valid=True))
SELECT a.name FROM a INNER JOIN b ON (a.id = b.a_id) WHERE NOT (b.valid = True)

2) Exclude with field lookup

A.objects.filter().exclude(b__valid=True)
SELECT a.name FROM a WHERE NOT 
    (a.id IN 
        (SELECT U1.a_id FROM b U1 WHERE 
            (U1.valid = True and U1.a_id IS NOT NULL)))

Is this normal behavior? It produces different queries and in result we can get different items from database. For example we have following database tables:

A
id    name
1     Seagull
2     Weasel
3     Deer

B
id    a_id    valid
1     1       1
1     1       0

First statement will return 1-Seagull object and second statement will return empty queryset. It doesn't look like correct behavior.

There is a simplified scheme of my models:

class A(Model):
   name = CharField()

class B(Model):
   a = models.ForeignKey(A, related_name='b', editable=False, null=False)
   valid = models.NullBooleanField(default=None)

So django generates two different queries for following statements:

1) Exclude with Q object

A.objects.filter().exclude(Q(b__valid=True))
SELECT a.name FROM a INNER JOIN b ON (a.id = b.a_id) WHERE NOT (b.valid = True)

2) Exclude with field lookup

A.objects.filter().exclude(b__valid=True)
SELECT a.name FROM a WHERE NOT 
    (a.id IN 
        (SELECT U1.a_id FROM b U1 WHERE 
            (U1.valid = True and U1.a_id IS NOT NULL)))

Is this normal behavior? It produces different queries and in result we can get different items from database. For example we have following database tables:

A
id    name
1     Seagull
2     Weasel
3     Deer

B
id    a_id    valid
1     1       1
1     1       0

First statement will return 1-Seagull object and second statement will return empty queryset. It doesn't look like correct behavior.

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