diff --git a/backend/app/analysis/common.py b/backend/app/analysis/common.py
index 3eb39865..b497e83f 100644
--- a/backend/app/analysis/common.py
+++ b/backend/app/analysis/common.py
@@ -107,22 +107,26 @@ def need(raw: Mapping[str, Any], key: str, what: str) -> Any:
 
 
 def written_places(raw: Any) -> int:
-    """快照里一格写到第几位小数（headline 是取整过的，按它的书写精度容差）：数字文本按字面，浮点按最短写法，整数为 0。"""
+    """快照里一格写到第几位小数（headline 是取整过的，按它的书写精度容差）：数字文本按字面，浮点按最短写法，整数为 0。是整数
+    的浮点（SQLite 的 ROUND() 交回 2120.0）是取到个位的，也为 0——最短写法里的「.0」不是书写精度。"""
     if isinstance(raw, bool) or raw is None:
         return 0
+    if isinstance(raw, float) and raw.is_integer():
+        return 0
     text = repr(raw) if isinstance(raw, float) else str(raw).strip()
     if "e" in text.lower():
         return 0
     return len(text.split(".", 1)[1]) if "." in text else 0
 
 
-def closes(total: Fraction, cell: Fraction, raw: Any) -> bool:
+def closes(total: Fraction, cell: Fraction, raw: Any, *, exact: bool = False) -> bool:
     """各段之和（或合起来的比率）和总数那一格对得上：十进制逐位相等；总数取整过的，差在它书写精度的半个末位以内也算；浮点
-    算出来的差在最后几位的也算（相对误差 1e-9 以内，同 engine/compare._equal）。"""
+    算出来的差在最后几位的也算（相对误差 1e-9 以内，同 engine/compare._equal）。exact：对的是上一层那一段算出来的精确值
+    （下钻），没有取整，只容浮点的最后几位。"""
     if total == cell:
         return True
     gap = abs(total - cell)
-    if gap <= Fraction(1, 2) / Fraction(10) ** written_places(raw):
+    if not exact and gap <= Fraction(1, 2) / Fraction(10) ** written_places(raw):
         return True
     scale = max(abs(total), abs(cell))
     return scale != 0 and gap <= scale * Fraction(1, 10 ** 9)
diff --git a/backend/app/analysis/decompose.py b/backend/app/analysis/decompose.py
index 18520067..8d09e453 100644
--- a/backend/app/analysis/decompose.py
+++ b/backend/app/analysis/decompose.py
@@ -345,7 +345,7 @@ def _additive_result(env: Env, params: dict[str, Any], used: list[str], segs: li
             gaps[side] = heads[side][0] - total
         if parent_row is not None:
             expect = to_fraction(parent_row.get(side))
-            if expect is None or not closes(total, expect, parent_row.get(side)):
+            if expect is None or not closes(total, expect, None, exact=True):
                 gaps.setdefault(side, (expect or Fraction(0)) - total)
     closed = not gaps
     deltas = {x.key: x.target - x.base for x in segs}
@@ -547,7 +547,7 @@ def _ratio_result(env: Env, params: dict[str, Any], used: list[str], segs: list[
                 "d_target": sum((x.target[1] for x in live), Fraction(0))}
         for col, total in sums.items():
             expect = to_fraction(parent_row.get(col))
-            if expect is None or not closes(total, expect, parent_row.get(col)):
+            if expect is None or not closes(total, expect, None, exact=True):
                 gaps.setdefault("base" if col.endswith("base") else "target", (expect or Fraction(0)) - total)
     closed = not gaps
     mix_total = sum((e[4] for e in effects), Fraction(0))
diff --git a/backend/tests/test_analysis_decompose.py b/backend/tests/test_analysis_decompose.py
index f651c35d..7cb21a10 100644
--- a/backend/tests/test_analysis_decompose.py
+++ b/backend/tests/test_analysis_decompose.py
@@ -127,6 +127,29 @@ async def test_a_rounded_headline_closes_within_its_written_precision():
         assert (result["verdict"]["code"] != "unclosed") is closes, written
 
 
+async def test_a_headline_rounded_by_the_database_to_a_whole_number_closes_within_half_a_unit():
+    # SQLite 的 ROUND() 交回浮点 2120.0：取到了个位，最短写法里的「.0」不是一位小数的书写精度
+    rows = [["华东", "2026-W41", "1120.2"], ["华东", "2026-W42", "700"], ["华北", "2026-W41", "1000.2"],
+            ["华北", "2026-W42", "600"]]
+    for written, closes in ((2120.0, True), (2121.0, False), (2120.5, False)):
+        head = snap("Q1", "SELECT ROUND(SUM(amount)) AS gmv FROM orders", ["gmv_base", "gmv"], [[written, 1300.0]])
+        result = await additive(rows, snaps=[weekly(rows), head], headline=["Q1.r0.gmv_base", "Q1.r0.gmv"])
+        assert (result["verdict"]["code"] != "unclosed") is closes, written
+
+
+async def test_a_drill_closes_against_the_exact_value_of_the_parent_segment():
+    top = await additive()                                             # 华东 820 → 700
+    near = snap("Q4", "SELECT province, week, SUM(amount) AS gmv FROM orders WHERE region = '华东' GROUP BY 1, 2",
+                ["province", "week", "gmv"],
+                [["沪", "2026-W41", "500.4"], ["沪", "2026-W42", "410"], ["苏", "2026-W41", 320],
+                 ["苏", "2026-W42", "290.3"]])
+    params = {"query": "Q4", "by": ["province"], "period": "week", "base": "2026-W41", "target": "2026-W42",
+              "measure": "gmv", "parent": {"of": "A3", "key": ["华东"]}}
+    off = await analyze("decompose", "additive", snaps=[near], parents={"A3": top}, **params)
+    # 上一层那一段是算出来的精确值，不是取整过的总数：820.4 对 820、700.3 对 700 都不闭合
+    assert off["verdict"]["code"] == "unclosed" and off["values"]["gap"] == "-0.4"
+
+
 async def test_drilling_down_checks_closure_against_the_parent_segment():
     top = await additive()
     province = snap("Q4", "SELECT province, week, SUM(amount) AS gmv FROM orders WHERE region = '华东' GROUP BY 1, 2",