fix(sql): guard FORCE_LIMIT against SHOW statements (#36939) (#42588)

Co-authored-by: Claude Code <noreply@anthropic.com>

tests/unit_tests/sql/parse_tests.py

@@ -2387,6 +2387,52 @@ def test_set_limit_value(
     assert statement.format() == expected
 
 
+@pytest.mark.parametrize(
+    "engine",
+    [
+        # Engines whose sqlglot dialect parses `SHOW` into a real `exp.Show`
+        # node (as opposed to falling back to an opaque `exp.Command`, which
+        # doesn't expose a `limit` arg and so was never affected by this bug).
+        "starrocks",
+        "mysql",
+        "snowflake",
+    ],
+)
+@pytest.mark.parametrize(
+    "sql",
+    [
+        "SHOW TABLES",
+        "SHOW DATABASES",
+        "SHOW CREATE TABLE test.will_test1",
+    ],
+)
+def test_set_limit_value_leaves_show_statements_unchanged(
+    sql: str, engine: str
+) -> None:
+    """
+    Regression for #36939: FORCE_LIMIT must not touch ``SHOW`` statements.
+
+    ``SHOW`` statements have no `LIMIT` clause in sqlglot's expression tree,
+    so forcing one via ``args["limit"]`` doesn't reject cleanly, it produces
+    a malformed statement with two ``LIMIT`` keywords (one from a stray
+    rendering of the bare ``Limit`` expression, one from the forced value).
+    StarRocks (and presumably other engines) reject that outright: "Getting
+    syntax error ... Unexpected input 'LIMIT'". The statement should be
+    left untouched instead, matching how ``SELECT`` statements without a
+    scannable row source aren't force-limited either.
+
+    Covers multiple engines, not just StarRocks: the fix guards on the AST
+    node type (``exp.Show``), not the dialect, so any engine whose sqlglot
+    dialect parses ``SHOW`` into a real ``Show`` node (e.g. MySQL, Snowflake)
+    is equally exposed and must be equally protected.
+    """
+    statement = SQLStatement(sql, engine)
+    original = statement.format()
+    statement.set_limit_value(1000, LimitMethod.FORCE_LIMIT)
+    assert statement.format() == original
+    assert "LIMIT" not in statement.format()
+
+
 @pytest.mark.parametrize(
     "kql, limit, expected",
     [