fix: support mixed ASC/DESC directions in ORDER BY

minidb/query.py

@@ -1,5 +1,6 @@
 """Query execution engine for MiniDB."""
 
+import functools
 import re
 from collections import defaultdict
 from typing import Any
@@ -364,29 +365,42 @@ def _project_columns(
         return results
 
     def _execute_order_by(self, rows: list[Row], order_by: list[OrderByItem]) -> list[Row]:
-        """Sort rows by ORDER BY columns."""
+        """Sort rows by ORDER BY columns with per-column direction."""
 
-        def sort_key(row):
-            keys = []
+        def _compare_rows(a: Row, b: Row) -> int:
             for item in order_by:
                 col_name = item.column
                 if item.table_alias:
                     col_name = f'{item.table_alias}.{item.column}'
 
-                val = row.get(col_name, row.get(item.column))
+                val_a = a.get(col_name, a.get(item.column))
+                val_b = b.get(col_name, b.get(item.column))
 
-                # Handle None values
-                if val is None:
-                    val = (1, None)  # Sort NULLs last
+                # NULLs sort last regardless of direction
+                if val_a is None and val_b is None:
+                    continue
+                if val_a is None:
+                    return 1
+                if val_b is None:
+                    return -1
+
+                # Compare values
+                if val_a < val_b:
+                    cmp = -1
+                elif val_a > val_b:
+                    cmp = 1
                 else:
-                    val = (0, val)
+                    continue
+
+                # Reverse for DESC
+                if item.direction == 'DESC':
+                    cmp = -cmp
+
+                return cmp
 
-                keys.append(val)
-            return keys
+            return 0
 
-        # Sort with direction handling
-        reverse = bool(order_by and order_by[0].direction == 'DESC')
-        return sorted(rows, key=sort_key, reverse=reverse)
+        return sorted(rows, key=functools.cmp_to_key(_compare_rows))
 
     def execute_insert(self, query: InsertQuery) -> int:
         """Execute an INSERT query."""

tests/test_queries.py

@@ -222,6 +222,23 @@ def test_order_by_desc(self, db):
         salaries = [r['salary'] for r in results]
         assert salaries == [55000.0, 52000.0, 50000.0, 48000.0, 45000.0]
 
+    def test_order_by_mixed_directions(self, db):
+        """Test ORDER BY with mixed ASC/DESC on different columns."""
+        # active has true/false, age varies within each group
+        results = db.query('SELECT * FROM users ORDER BY active DESC, age ASC')
+
+        # active=true first (DESC), then within each group sorted by age ASC
+        active_flags = [r['active'] for r in results]
+        assert active_flags == [True, True, True, False, False]
+
+        # Ages within active=true group should be ascending
+        active_ages = [r['age'] for r in results if r['active'] is True]
+        assert active_ages == sorted(active_ages)
+
+        # Ages within active=false group should be ascending
+        inactive_ages = [r['age'] for r in results if r['active'] is False]
+        assert inactive_ages == sorted(inactive_ages)
+
     def test_order_by_with_where(self, db):
         """Test ORDER BY combined with WHERE."""
         results = db.query('SELECT * FROM users WHERE active = true ORDER BY age DESC')