class Substr(expression, pos, length=None, **extra) [source]
Returns a substring of length length from the field or expression starting at position pos. The position is 1-indexed, so the position must be greater than 0. If length is None, then the rest of the string will be returned.
Usage example:
>>> # Set the alias to the first 5 characters of the name as lowercase
>>> from django.db.models.functions import Substr, Lower
>>> Author.objects.create(name='Margaret Smith')
>>> Author.objects.update(alias=Lower(Substr('name', 1, 5)))
1
>>> print(Author.objects.get(name='Margaret Smith').alias)
marga
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