perf: /history 消除题材查询 N+1 并修正排序注释

Co-Authored-By: Claude <noreply@anthropic.com>

backend/routes/core_stocks.py

@@ -52,7 +52,7 @@ async def active_core_stocks():
                 s["lastAppear"] = r["trade_date"]
 
         stocks = list(stock_days.values())
-        # 稳定排序：先按最近上榜日降序，再按出现次数降序
+        # 稳定排序：先按出现次数降序，再按最近上榜日降序
         stocks.sort(key=lambda x: x.get("lastAppear") or "", reverse=True)
         stocks.sort(key=lambda x: -x["appearCount"])
         return JSONResponse({"dates": dates, "stocks": stocks}, headers=_NO_CACHE_HEADERS)
@@ -67,14 +67,20 @@ async def core_stock_history(date: str = Query(..., description="交易日 YYYY-
         rows = conn.execute(
             "SELECT * FROM daily_core_stocks WHERE trade_date = ? ORDER BY rank ASC", (date,)
         ).fetchall()
+        # 一次性取该日全部题材关联，按 stock_code 分组，避免逐股 N+1 查询
+        themes_rows = conn.execute(
+            "SELECT stock_code, theme_code, theme_name FROM daily_core_stock_themes WHERE trade_date = ?",
+            (date,),
+        ).fetchall()
+        themes_by_stock: dict[str, list] = {}
+        for t in themes_rows:
+            themes_by_stock.setdefault(t["stock_code"], []).append(
+                {"theme_code": t["theme_code"], "theme_name": t["theme_name"]}
+            )
         items = []
         for r in rows:
             d = dict_from_row(r)
-            themes = conn.execute(
-                "SELECT theme_code, theme_name FROM daily_core_stock_themes WHERE trade_date = ? AND stock_code = ?",
-                (date, d["stock_code"]),
-            ).fetchall()
-            d["themes"] = [dict(t) for t in themes]
+            d["themes"] = themes_by_stock.get(d["stock_code"], [])
             items.append(d)
         return JSONResponse({"date": date, "items": items}, headers=_NO_CACHE_HEADERS)
     finally: