fix: skip aggregate pushdown when a WHERE clause stays local

[breken-ai]

What kind of change does this PR introduce?

Bug fix (aggregate pushdown, supabase-wrappers/src/upper.rs).

What is the current behavior?

When the framework can't turn a WHERE clause into a Qual, Postgres normally evaluates it locally on each scanned row. Examples are lower(name) = 'x', a > b, or any function or expression on the column side.

get_foreign_upper_paths offers the aggregate path without checking for such clauses. That path is a bare ForeignScan on the upper rel with no local filter. So the remote aggregate runs without the clause and Postgres returns its result as final:

-- mysql_agg.orders has 5 rows, one of them Carol
SELECT count(*) FROM mysql_agg.orders WHERE lower(name) = 'carol';
-- returns 5, expected 1

This affects every FDW that supports aggregate pushdown (MySQL, ClickHouse, BigQuery). When only some clauses can be pushed, the pushable ones are applied and the rest are silently dropped. For example, status = 'inactive' AND lower(name) = 'eve' sums every inactive order.

What is the new behavior?

The aggregate path is only offered when every restriction clause on the foreign table was extracted as a qual (state.quals.len() equals the length of input_rel->baserestrictinfo). Otherwise the planner uses the normal scan with a local filter and a local Aggregate, so the result is correct. Queries whose WHERE clauses are all pushable are pushed down exactly as before.

Additional context

• Tests: new cases in mysql_fdw/tests.rs (mysql_aggregate_pushdown_test) check both results and plans:
  • COUNT(*) ... WHERE lower(name) = 'carol' returns 1 and is not pushed down.
  • SUM(amount) ... WHERE status = 'inactive' AND lower(name) = 'eve' returns 150 and is not pushed down.
• Red/green: cargo pgrx test pg17 mysql --features mysql_fdw against a mysql:8.4 container.
  • On main the new assertion fails with expected 1, got 5.
  • With this change all 3 mysql tests pass.
• Checks: cargo fmt --check passes, and cargo clippy --tests -D warnings (pg17, mysql_fdw) is clean.
• The existing pushed-down cases with simple WHERE clauses (id = 1, amount > 75, id IN (...)) are unaffected.
• Full-query pushdown support for FDW #615 (full-query pushdown) computes a similar "unpushed quals" signal for its new path. It does not change the existing aggregate path, so the two don't overlap.

This PR was prepared with AI assistance (Claude). I reproduced the failure and ran the tests locally as described above.

🤖 Generated with Claude Code

[imor]

Closing as this is 100% AI generated.