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fix(query): count and restrict expressions with an empty primary key - #1605
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An expression with an empty primary key, such as `dj.U() & T` or `dj.U().aggr(T, n="count(*)")`, holds at most one row. Two operations on such expressions failed: - `len()` took the single-column branch and generated `count(DISTINCT )`, which is invalid SQL. It now returns 0 or 1 by checking whether the row exists. - Restricting a `dj.U()` aggregation hit a bare assert in `Aggregation.make_sql`. Removing the assert alone would not have been enough: the MySQL branch emitted HAVING only together with GROUP BY, so the restriction would have been dropped without notice. MySQL now emits HAVING without GROUP BY, and PostgreSQL takes the subquery path whenever the aggregation is restricted, with or without grouping attributes. Restriction conditions on an aggregation are now joined with str(), as the base where_clause already does, so restricting any aggregation by False no longer raises TypeError. Closes #1581 Closes #1580
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October 17, 2026 22:02
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An expression with an empty primary key, such as
dj.U() & Tordj.U().aggr(T, n="count(*)"), holds at most one row. Two operations onsuch expressions failed:
len()took the single-column branch and generatedcount(DISTINCT ), which is invalid SQL. It now returns 0 or 1 bychecking whether the row exists.
dj.U()aggregation hit a bare assert inAggregation.make_sql. Removing the assert alone would not have beenenough: the MySQL branch emitted HAVING only together with GROUP BY,
so the restriction would have been dropped without notice. MySQL now
emits HAVING without GROUP BY, and PostgreSQL takes the subquery path
whenever the aggregation is restricted, with or without grouping
attributes.
Restriction conditions on an aggregation are now joined with str(), as
the base where_clause already does, so restricting any aggregation by
False no longer raises TypeError.
Closes #1581
Closes #1580