diff --git a/backend/README.md b/backend/README.md
index b6dbbb6d3..c854cfb8a 100644
--- a/backend/README.md
+++ b/backend/README.md
@@ -1 +1,49 @@
-# FastAPI Project - Backend
\ No newline at end of file
+# FastAPI Project - Backend
+
+## Table sample data in SQL generation
+
+`TABLE_SAMPLE_DATA_ENABLED` controls whether SQLBot fetches table sample rows
+and includes them in SQL-generation prompts. It defaults to `true` to preserve
+existing behavior, including the current three-row sample limit.
+
+To disable automatic sampling, set the following environment variable (or add it
+to the project-root `.env` used when running the backend from `backend/`):
+
+```dotenv
+TABLE_SAMPLE_DATA_ENABLED=false
+```
+
+For Docker Compose, pass it explicitly to the SQLBot service:
+
+```yaml
+environment:
+  TABLE_SAMPLE_DATA_ENABLED: "false"
+```
+
+A Compose `.env` file alone does not automatically pass all its variables into a
+container. For `docker run`, use `-e TABLE_SAMPLE_DATA_ENABLED=false`.
+Settings are loaded at process startup: restart a source deployment, or recreate
+the container with the new environment configuration.
+
+When disabled, the automatic sample-data helper returns before reading table
+metadata or sample rows. The SQL prompt template also ignores pre-existing
+`sample_data` values. Schema context, explicit SQL queries, manual data previews
+and their existing permission checks remain unchanged. Less sample context may
+affect SQL-generation quality.
+
+This is not a global data-loss-prevention switch. User messages, field comments,
+SQL examples, query results and analysis prompts can still contain business
+data. Existing logs are not deleted or retroactively redacted.
+
+### Focused regression tests
+
+From the repository root, with the backend development dependencies available:
+
+```bash
+python -m pytest -q tests/test_table_sample_data.py
+```
+
+The tests execute actual source function definitions with dependency doubles to
+avoid initializing database drivers, embedding models or X-Pack. They cover
+configuration parsing, sampling, prompt rendering and unaffected query/preview
+behavior; they are not full application or model-provider integration tests.
diff --git a/backend/apps/datasource/crud/datasource.py b/backend/apps/datasource/crud/datasource.py
index 11720a783..3d394ce92 100644
--- a/backend/apps/datasource/crud/datasource.py
+++ b/backend/apps/datasource/crud/datasource.py
@@ -500,6 +500,9 @@ def get_table_sample_data(ds: CoreDatasource, table_name: str, fields: list) ->
 def get_tables_sample_data(session: SessionDep, current_user: CurrentUser, ds: CoreDatasource,
                            table_list: list[str] = None) -> str:
     """Get sample data (3 rows) for all tables to help AI understand the data"""
+    if not settings.TABLE_SAMPLE_DATA_ENABLED:
+        return ""
+
     table_objs = get_table_obj_by_ds(session=session, current_user=current_user, ds=ds)
     if len(table_objs) == 0:
         return ""
diff --git a/backend/apps/template/generate_sql/generator.py b/backend/apps/template/generate_sql/generator.py
index 07eb61972..a13f3bb64 100644
--- a/backend/apps/template/generate_sql/generator.py
+++ b/backend/apps/template/generate_sql/generator.py
@@ -2,11 +2,17 @@
 
 from apps.db.constant import DB
 from apps.template.template import get_base_template, get_sql_template as get_base_sql_template
+from common.core.config import settings
 
 
 def get_sql_template():
     template = get_base_template()
-    return template['template']['sql']
+    sql_template = template['template']['sql']
+    if not settings.TABLE_SAMPLE_DATA_ENABLED:
+        # Do not mutate shared templates or render pre-existing sample values.
+        sql_template = sql_template.copy()
+        sql_template['generate_basic_info'] = sql_template['generate_basic_info'].replace('{sample_data}', '')
+    return sql_template
 
 
 def get_sql_example_template(db_type: Union[str, DB]):
diff --git a/backend/common/core/config.py b/backend/common/core/config.py
index 4b9baeaec..a350e5b77 100644
--- a/backend/common/core/config.py
+++ b/backend/common/core/config.py
@@ -126,6 +126,9 @@ def SQLALCHEMY_DATABASE_URI(self) -> PostgresDsn | str:
     PG_POOL_RECYCLE: int = 3600
     PG_POOL_PRE_PING: bool = True
 
+    # Include table sample rows in SQL generation context (disable for sensitive data).
+    TABLE_SAMPLE_DATA_ENABLED: bool = True
+
     TABLE_EMBEDDING_ENABLED: bool = True
     TABLE_EMBEDDING_COUNT: int = 10
     DS_EMBEDDING_COUNT: int = 10
@@ -138,6 +141,7 @@ def SQLALCHEMY_DATABASE_URI(self) -> PostgresDsn | str:
                      'PARSE_REASONING_BLOCK_ENABLED',
                      'PG_POOL_PRE_PING',
                      'TABLE_EMBEDDING_ENABLED',
+                     'TABLE_SAMPLE_DATA_ENABLED',
                      mode='before')
     @classmethod
     def lowercase_bool(cls, v: Any) -> Any:
diff --git a/tests/test_table_sample_data.py b/tests/test_table_sample_data.py
new file mode 100644
index 000000000..bc2512a16
--- /dev/null
+++ b/tests/test_table_sample_data.py
@@ -0,0 +1,241 @@
+"""Isolated regression tests for the table-sample context switch (#1291).
+
+Load function definitions from the actual sources, not copied implementations.
+This avoids importing database drivers, embedding models and X-Pack just to test
+sampling and prompt construction. Settings uses the real Pydantic loader. These
+are unit tests, not full application or model-provider integration tests.
+"""
+
+import __future__
+import ast
+import importlib.util
+import json
+from copy import deepcopy
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock, Mock
+
+import pytest
+from pydantic import ValidationError
+
+ROOT = Path(__file__).resolve().parents[1]
+BACKEND = ROOT / "backend"
+SENTINEL = "SQLBOT_SAMPLE_SENTINEL_1291"
+
+
+def load_functions(relative_path, names, namespace):
+    """Execute unchanged source definitions with explicit dependency doubles."""
+    path = BACKEND / relative_path
+    source = ast.parse(path.read_text(encoding="utf-8"), filename=str(path))
+    definitions = [
+        node for node in source.body
+        if isinstance(node, ast.FunctionDef) and node.name in names
+    ]
+    assert {node.name for node in definitions} == set(names)
+    module = ast.Module(body=definitions, type_ignores=[])
+    code = compile(
+        module, str(path), "exec", flags=__future__.annotations.compiler_flag,
+        dont_inherit=True,
+    )
+    exec(code, namespace)
+    return namespace
+
+
+@pytest.fixture
+def settings_class(monkeypatch, tmp_path):
+    # Do not load a developer's .env or carry a previous test's configuration.
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.delenv("TABLE_SAMPLE_DATA_ENABLED", raising=False)
+    spec = importlib.util.spec_from_file_location(
+        "sqlbot_test_settings", BACKEND / "common/core/config.py"
+    )
+    module = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(module)
+    return module.Settings
+
+
+def test_sample_context_is_enabled_by_default(settings_class):
+    assert settings_class(_env_file=None).TABLE_SAMPLE_DATA_ENABLED is True
+
+
+@pytest.mark.parametrize("value, expected", [
+    ("true", True), ("false", False), ("TRUE", True), ("FALSE", False),
+    (" True ", True), (" False ", False), ("1", True), ("0", False),
+])
+def test_environment_boolean_parsing(settings_class, monkeypatch, value, expected):
+    monkeypatch.setenv("TABLE_SAMPLE_DATA_ENABLED", value)
+    assert settings_class(_env_file=None).TABLE_SAMPLE_DATA_ENABLED is expected
+
+
+def test_invalid_boolean_is_rejected(settings_class, monkeypatch):
+    monkeypatch.setenv("TABLE_SAMPLE_DATA_ENABLED", "not-a-boolean")
+    with pytest.raises(ValidationError):
+        settings_class(_env_file=None)
+
+
+def test_dotenv_can_disable_sample_context(settings_class, tmp_path):
+    env_file = tmp_path / "sample.env"
+    env_file.write_text("TABLE_SAMPLE_DATA_ENABLED=false\n", encoding="utf-8")
+    assert settings_class(_env_file=env_file).TABLE_SAMPLE_DATA_ENABLED is False
+
+
+@pytest.fixture
+def sampling():
+    fields = [SimpleNamespace(
+        field_name="sku", field_type="varchar", custom_comment="Product code",
+    )]
+    table = SimpleNamespace(
+        id=1, table_name="orders", custom_comment="Order records", embedding=None,
+    )
+    table_obj = SimpleNamespace(schema="shop", table=table, fields=fields)
+    namespace = {
+        "settings": SimpleNamespace(
+            TABLE_SAMPLE_DATA_ENABLED=True, TABLE_EMBEDDING_ENABLED=False,
+        ),
+        "get_table_obj_by_ds": Mock(return_value=[table_obj]),
+        "exec_sql": Mock(return_value={"data": [{"sku": SENTINEL}]}),
+        "DB": SimpleNamespace(get_db=lambda _: SimpleNamespace(prefix='"', suffix='"')),
+        "equals_ignore_case": lambda first, second: first.lower() == second.lower(),
+    }
+    return load_functions(
+        "apps/datasource/crud/datasource.py",
+        {"get_tables_sample_data", "get_table_sample_data", "get_table_schema", "execSql", "preview"},
+        namespace,
+    )
+
+
+def test_disabled_does_not_read_metadata_or_rows(sampling):
+    sampling["settings"].TABLE_SAMPLE_DATA_ENABLED = False
+    result = sampling["get_tables_sample_data"](
+        object(), object(), SimpleNamespace(type="pg"),
+    )
+    assert result == ""
+    sampling["get_table_obj_by_ds"].assert_not_called()
+    sampling["exec_sql"].assert_not_called()
+
+
+def test_enabled_preserves_sample_query_and_output(sampling):
+    session, user = object(), object()
+    datasource = SimpleNamespace(type="pg")
+    result = sampling["get_tables_sample_data"](session, user, datasource)
+    sampling["get_table_obj_by_ds"].assert_called_once_with(
+        session=session, current_user=user, ds=datasource,
+    )
+    sampling["exec_sql"].assert_called_once_with(
+        ds=datasource, sql='SELECT "sku" FROM "orders" LIMIT 3', origin_column=True,
+    )
+    assert result == '# Table: orders\n[\n  {\n    "sku": "' + SENTINEL + '"\n  }\n]'
+
+
+@pytest.mark.parametrize("table_list", [[], ["another_table"]])
+def test_selected_table_filter_is_preserved(sampling, table_list):
+    assert sampling["get_tables_sample_data"](
+        object(), object(), SimpleNamespace(type="pg"), table_list,
+    ) == ""
+    sampling["exec_sql"].assert_not_called()
+
+
+def test_no_authorized_fields_does_not_sample(sampling):
+    sampling["get_table_obj_by_ds"].return_value[0].fields = []
+    assert sampling["get_tables_sample_data"](
+        object(), object(), SimpleNamespace(type="pg"),
+    ) == ""
+    sampling["exec_sql"].assert_not_called()
+
+
+def test_sample_limit_remains_three_rows(sampling):
+    sampling["exec_sql"].return_value = {"data": [{"sku": n} for n in range(5)]}
+    result = sampling["get_tables_sample_data"](
+        object(), object(), SimpleNamespace(type="pg"),
+    )
+    assert json.loads(result.split("\n", 1)[1]) == [{"sku": 0}, {"sku": 1}, {"sku": 2}]
+
+
+def test_disabled_does_not_remove_schema(sampling):
+    sampling["settings"].TABLE_SAMPLE_DATA_ENABLED = False
+    schema, tables = sampling["get_table_schema"](
+        object(), object(), SimpleNamespace(type="pg", table_relation=None),
+        "Show orders", embedding=False,
+    )
+    assert tables == ["orders"]
+    assert "shop.orders" in schema
+    assert "sku:varchar, Product code" in schema
+    sampling["exec_sql"].assert_not_called()
+
+
+def test_disabled_does_not_block_explicit_sql_execution(sampling):
+    sampling["settings"].TABLE_SAMPLE_DATA_ENABLED = False
+    sampling["CoreDatasource"] = SimpleNamespace(id=1)
+    sampling["select"] = Mock()
+    session, datasource = Mock(), object()
+    session.exec.return_value.first.return_value = datasource
+    result = sampling["execSql"](session, 1, "SELECT 1")
+    sampling["exec_sql"].assert_called_once_with(datasource, "SELECT 1", True)
+    assert result is sampling["exec_sql"].return_value
+
+
+@pytest.fixture
+def templates():
+    template = {"template": {"sql": {
+        "generate_basic_info": (
+            "<db-engine>{engine}</db-engine>\n<schema>{schema}</schema>\n"
+            "<sample-data>{sample_data}</sample-data>"
+        ),
+        "other_rule": "Preserve other rules",
+    }}}
+    namespace = {
+        "settings": SimpleNamespace(TABLE_SAMPLE_DATA_ENABLED=True),
+        "get_base_template": Mock(return_value=template),
+    }
+    return load_functions(
+        "apps/template/generate_sql/generator.py", {"get_sql_template"}, namespace,
+    )
+
+
+@pytest.mark.parametrize("enabled", [True, False])
+def test_template_controls_sample_insertion_without_removing_schema(templates, enabled):
+    templates["settings"].TABLE_SAMPLE_DATA_ENABLED = enabled
+    result = templates["get_sql_template"]()
+    rendered = result["generate_basic_info"].format(
+        engine="PostgreSQL", schema="orders(sku varchar)", sample_data=SENTINEL,
+    )
+    assert (SENTINEL in rendered) is enabled
+    assert "PostgreSQL" in rendered
+    assert "orders(sku varchar)" in rendered
+    assert result["other_rule"] == "Preserve other rules"
+
+
+def test_disabling_does_not_mutate_shared_templates(templates):
+    original = deepcopy(templates["get_base_template"].return_value)
+    templates["settings"].TABLE_SAMPLE_DATA_ENABLED = False
+    disabled = templates["get_sql_template"]()
+    assert "{sample_data}" not in disabled["generate_basic_info"]
+    assert templates["get_base_template"].return_value == original
+    templates["settings"].TABLE_SAMPLE_DATA_ENABLED = True
+    assert "{sample_data}" in templates["get_sql_template"]()["generate_basic_info"]
+
+
+def test_disabled_does_not_block_manual_preview(sampling):
+    sampling["settings"].TABLE_SAMPLE_DATA_ENABLED = False
+    sampling.update({
+        "CoreDatasource": MagicMock(), "CoreField": MagicMock(), "CoreTable": MagicMock(),
+        "is_normal_user": Mock(return_value=False),
+        "get_engine_config": Mock(return_value=SimpleNamespace(dbSchema="public")),
+    })
+    datasource = SimpleNamespace(type="excel")
+    field = SimpleNamespace(field_name="sku", checked=True)
+    table = SimpleNamespace(id=1, table_name="orders")
+    ds_query, field_query, table_query = Mock(), Mock(), Mock()
+    ds_query.filter.return_value.first.return_value = datasource
+    field_query.filter.return_value.order_by.return_value.all.return_value = [field]
+    table_query.filter.return_value.first.return_value = table
+    session = Mock()
+    session.query.side_effect = [ds_query, field_query, table_query]
+    result = sampling["preview"](session, object(), 1, SimpleNamespace(table=table))
+    sampling["exec_sql"].assert_called_once()
+    args = sampling["exec_sql"].call_args.args
+    assert args[0] is datasource
+    assert '"public"."orders"' in args[1]
+    assert "LIMIT 100" in args[1]
+    assert args[2] is True
+    assert result is sampling["exec_sql"].return_value