#25470: Django cast DATE field to DATETIME unexpectedly
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Reporter: stanleyxu2005 | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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I posted a question at http://stackoverflow.com/questions/32795047/have-a
-perforamance-issue-of-query-date-object-using-django-queryset
I'm using django 1.8.4 writing a webapp. The backend uses MySQL 5.6
(MyISAM). Recently the number of table records reaches 1 million, it will
take 1-1.5 seconds to query all distinct record dates. But using MySQL
client, it takes less than 0.001 second.
'''Django Code'''
{{{
class Model1(models.Model):
date = models.DateField(db_index=True)
# benchmark code
db_dates = set(Model1.objects.dates("date", kind="day"))
}}}
I dumped the django queries.
{{{
[{u'time': u'0.000', u'sql': u'SET SQL_AUTO_IS_NULL = 0'},
{u'time': u'1.989', u'sql': u"SELECT DISTINCT
CAST(DATE_FORMAT(`model1_table`.`date`, '%Y-%m-%d 00:00:00') AS DATETIME)
AS `datefield` FROM `model1_table` WHERE `model1_table`.`date` IS NOT NULL
ORDER BY `datefield` ASC"}
]
}}}
Actually the second query did a type cast. This is the root cause of the
slow.
I'd like to know, why django cast DATE to DATETIME. Is it a bug?
--
Ticket URL: <https://code.djangoproject.com/ticket/25470>
Django <https://code.djangoproject.com/>
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