Support select and explain for UNION queries

Some UNION queries can start with "(", causing it to not be
classified as a SELECT query, and consequently the select and
explain buttons are missing on the SQL panel.

debug_toolbar/panels/sql/forms.py

@@ -5,7 +5,7 @@
 from django.db import connections
 from django.utils.functional import cached_property
 
-from debug_toolbar.panels.sql.utils import reformat_sql
+from debug_toolbar.panels.sql.utils import is_select_query, reformat_sql
 
 
 class SQLSelectForm(forms.Form):
@@ -27,7 +27,7 @@ class SQLSelectForm(forms.Form):
     def clean_raw_sql(self):
         value = self.cleaned_data["raw_sql"]
 
-        if not value.lower().strip().startswith("select"):
+        if not is_select_query(value):
             raise ValidationError("Only 'select' queries are allowed.")
 
         return value

debug_toolbar/panels/sql/panel.py

@@ -12,7 +12,11 @@
 from debug_toolbar.panels.sql import views
 from debug_toolbar.panels.sql.forms import SQLSelectForm
 from debug_toolbar.panels.sql.tracking import wrap_cursor
-from debug_toolbar.panels.sql.utils import contrasting_color_generator, reformat_sql
+from debug_toolbar.panels.sql.utils import (
+    contrasting_color_generator,
+    is_select_query,
+    reformat_sql,
+)
 from debug_toolbar.utils import render_stacktrace
 
 
@@ -266,9 +270,7 @@ def generate_stats(self, request, response):
                     query["sql"] = reformat_sql(query["sql"], with_toggle=True)
 
                 query["is_slow"] = query["duration"] > sql_warning_threshold
-                query["is_select"] = (
-                    query["raw_sql"].lower().lstrip().startswith("select")
-                )
+                query["is_select"] = is_select_query(query["raw_sql"])
 
                 query["rgb_color"] = self._databases[alias]["rgb_color"]
                 try:

debug_toolbar/panels/sql/utils.py

@@ -86,6 +86,11 @@ def process(stmt):
         return "".join(escaped_value(token) for token in stmt.flatten())
 
 
+def is_select_query(sql):
+    # UNION queries can start with "(".
+    return sql.lower().lstrip(" (").startswith("select")
+
+
 def reformat_sql(sql, *, with_toggle=False):
     formatted = parse_sql(sql)
     if not with_toggle:

docs/changes.rst

@@ -3,6 +3,7 @@ Change log
 
 Pending
 -------
+* Support select and explain buttons for ``UNION`` queries on PostgreSQL.
 
 4.4.6 (2024-07-10)
 ------------------

tests/panels/test_sql.py

@@ -729,6 +729,16 @@ def test_similar_and_duplicate_grouping(self):
         self.assertNotEqual(queries[0]["similar_color"], queries[3]["similar_color"])
         self.assertNotEqual(queries[0]["duplicate_color"], queries[3]["similar_color"])
 
+    @unittest.skipUnless(
+        connection.vendor == "postgresql", "Test valid only on PostgreSQL"
+    )
+    def test_explain(self):
+        list(User.objects.filter(id__lt=20).union(User.objects.filter(id__gt=10)))
+        response = self.panel.process_request(self.request)
+        self.panel.generate_stats(self.request, response)
+        query = self.panel._queries[0]
+        self.assertTrue(query["is_select"])
+
 
 class SQLPanelMultiDBTestCase(BaseMultiDBTestCase):
     panel_id = "SQLPanel"

tests/test_integration.py

@@ -432,6 +432,26 @@ def test_sql_explain_checks_show_toolbar(self):
             )
             self.assertEqual(response.status_code, 404)
 
+    @unittest.skipUnless(
+        connection.vendor == "postgresql", "Test valid only on PostgreSQL"
+    )
+    def test_sql_explain_union_query(self):
+        url = "/__debug__/sql_explain/"
+        data = {
+            "signed": SignedDataForm.sign(
+                {
+                    "sql": "(SELECT * FROM auth_user) UNION (SELECT * from auth_user)",
+                    "raw_sql": "(SELECT * FROM auth_user) UNION (SELECT * from auth_user)",
+                    "params": "{}",
+                    "alias": "default",
+                    "duration": "0",
+                }
+            )
+        }
+
+        response = self.client.post(url, data)
+        self.assertEqual(response.status_code, 200)
+
     @unittest.skipUnless(
         connection.vendor == "postgresql", "Test valid only on PostgreSQL"
     )