#29527: Multi-column comparisons
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Reporter: Ryan Hiebert | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 2.0
Severity: Normal | Keywords: QuerySet.extra
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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Multi-column comparisons
In order to implement keyset pagination, AKA the seek method, across
multiple fields including ordering on non-unique fields, I'm wanting to
write a PostgreSQL that compares multiple fields in an ordered fashion. To
my knowledge this isn't possible with the current ORM syntax. My
particular use-case further complicates this by also wanting a subquery in
order to avoid serializing more than the unique key in the response.
Here's a generic example where clause that mirrors my use-case:
{{{#!sql
(a,b,c,id) > (SELECT a,b,c,id FROM mytable WHERE id = ?)
}}}
What this does special is account for all of the columns when making the
comparison. So it will only compare the id column if all of the a, b, and
c columns are the same, to allow for exact indentification in an arbitrary
ordering.
In the PostgreSQL docs this feature is called Row Constructor Comparison,
and the documentation is here: https://www.postgresql.org/docs/9.6/static
/functions-comparisons.html#ROW-WISE-COMPARISON.
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Ticket URL: <https://code.djangoproject.com/ticket/29527>
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