diff --git a/backend/app/data/introspect.py b/backend/app/data/introspect.py
index 27ab77e1..ea8875be 100644
--- a/backend/app/data/introspect.py
+++ b/backend/app/data/introspect.py
@@ -447,6 +447,15 @@ def describe_table(source: Any, table: str, *, catalog: Mapping[str, Mapping[str
         available = "、".join(
             m.get("qualified", n) for n, m in list(tables.items())[:30]
         )
+        if cache.get("truncated"):
+            # 只探查了一部分表：没探查到不等于没有。以前照样回「中没有 X」，模型据此换了别的表或者编答案
+            total = cache.get("total")
+            of = f"共 {total} 个对象，" if isinstance(total, int) else ""
+            return (
+                f"数据源「{source.name}」{of}只探查了其中 {len(tables)} 个，{table} 不在已探查的范围内，"
+                "无法判断是否存在。请直接查询数据字典（information_schema.tables / columns，SQLite 用 "
+                f"sqlite_master）确认它的结构。已探查的对象包括：{available}"
+            )
         return f"数据源「{source.name}」中没有 {table}。现有的对象：{available}"
 
     head = f"{'视图' if meta.get('is_view') else '表'} {meta.get('qualified', table)}"
diff --git a/backend/tests/test_catalog_schema_truncated.py b/backend/tests/test_catalog_schema_truncated.py
index b16489d2..4477b7f8 100644
--- a/backend/tests/test_catalog_schema_truncated.py
+++ b/backend/tests/test_catalog_schema_truncated.py
@@ -114,3 +114,20 @@ async def test_assistant_context_of_a_complete_schema_says_nothing_extra(narrow)
     (row,) = ctx.op()["sources"]
     assert row["total"] == 3 and "explored" not in row
     assert "没有探查到" not in ctx.section()
+
+
+async def test_schema_tool_does_not_deny_a_table_that_was_not_introspected(wide, narrow):
+    """只探查了一部分表时，查一张没探查到的表不能说「没有」：它可能就在没探查到的那部分里。
+    以前回「数据源中没有 X」，模型据此改用别的表，或者编一个答案。"""
+    from app.data.introspect import describe_table
+
+    row = await _row(wide[0])
+    explored = set((row.schema_cache or {}).get("tables") or {})
+    missing = next(f"t{i:03d}" for i in range(WIDE) if f"t{i:03d}" not in explored)
+    text = describe_table(row, missing)
+    assert "中没有" not in text
+    assert "只探查了" in text and "information_schema" in text
+
+    # 探查完整的库：查不存在的表照旧说没有
+    small = await _row(narrow[0])
+    assert "中没有 nope" in describe_table(small, "nope")