#31792: Use `EXISTS(SELECT 1 ...)` for subqueries
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Reporter: w0rp | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 3.0
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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If you write a QuerySet call like so in Django...
{{{
MyModel.objects.all().exists()
}}}
the query run will be like so.
{{{
SELECT 1 AS "a" FROM "myapp_mymodel" LIMIT 1;
}}}
If you use the `Exists()` function to filter with a subquery like so...
{{{
MyModel.objects.filter(Exists(MyOtherModel.objects.all()))
}}}
The subquery will be run like so.
{{{
... WHERE EXISTS(SELECT "myapp_myothermodel"."id", ... FROM
"myapp_myothermodel");
}}}
It would be nice if the queries generated for `Exists()` used `SELECT 1`
like `.exists()` does, where possible. In an app I work on, I have one
query in particular that is 15KB in size, but only around 8KB if I apply
`.annotate(_1=Value(1, output_field=IntegerField())).values_list('_1')` to
all of the subqueries. That change alone is enough to make my queries much
easier to debug.
--
Ticket URL: <https://code.djangoproject.com/ticket/31792>
Django <https://code.djangoproject.com/>
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