Code Review for SQL

## SQL PR Review Checklist (copy into review comment)
 
### Migrations
- [ ] Version unique; filename has ticket ID
- [ ] Lock risk: low / medium / high (Migration Safety Skill)
- [ ] CONCURRENTLY for prod index on large tables
- [ ] Rollback SQL in db/rollback/ or PR body
- [ ] Deploy order: migration before app
 
### Queries
- [ ] EXPLAIN (ANALYZE, BUFFERS) on staging attached
- [ ] No seq scan regression on large tables
- [ ] Parameterized queries ($1 / named binds)
- [ ] LIMIT on list endpoints
 
### Security
- [ ] Role least privilege (not superuser)
- [ ] search_path set or schema-qualified names
- [ ] RLS policies if tenant table

EXPLAIN (ANALYZE, BUFFERS)
SELECT id, total, created_at
FROM orders
WHERE tenant_id = $1 AND status = 'open'
ORDER BY created_at DESC
LIMIT 100;

Index Scan using idx_orders_tenant_status on orders
  Buffers: shared hit=120 read=4
  Execution Time: 1.2 ms

SELECT * FROM orders WHERE tenant_id = $1 OR tenant_id = $2;
-- No EXPLAIN, no LIMIT, OR prevents index on some planners

Request changes:
1. Attach EXPLAIN (ANALYZE, BUFFERS) from staging
2. Replace OR with IN (...) or UNION ALL pattern
3. List columns explicitly; drop SELECT *
4. See EXPLAIN Review Skill for pass/fail rubric

# BAD: N+1
for order in orders:
    items = session.query(Item).filter_by(order_id=order.id).all()
 
# GOOD: joinedload evidence in PR
orders = session.query(Order).options(joinedload(Order.items)).filter(...)

-- rollback/V20260709_128__orders_priority_down.sql
DROP INDEX CONCURRENTLY IF EXISTS idx_orders_priority;
ALTER TABLE orders DROP COLUMN IF EXISTS priority;