From 8e7863b603ca37cb9d24e874dc555f754289e86d Mon Sep 17 00:00:00 2001
From: Maha Rana Yadavalli <271375718+maharanay22@users.noreply.github.com>
Date: Fri, 16 Oct 2026 20:33:56 -0400
Subject: [PATCH] Fail the PostgreSQL connection when the configured schema
 doesn't exist

The handler ran SET search_path TO "<schema>", public without checking
that the schema exists. PostgreSQL accepts a search_path entry for a
missing schema, so a mistyped or wrong-cased schema (for example "sales"
when the real schema is "Sales") made every unqualified query silently
read tables from public, and check_connection still reported success.

Look the schema up in pg_namespace before setting search_path and raise
InvalidSchemaName when it is missing, so connect() and check_connection()
fail with a clear message. Also close the connection when setup fails
after psycopg.connect() succeeded.
---
 .../postgres_handler/postgres_handler.py      |  8 ++++++
 tests/unit/handlers/test_postgres.py          | 28 ++++++++++++++++++-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/mindsdb/integrations/handlers/postgres_handler/postgres_handler.py b/mindsdb/integrations/handlers/postgres_handler/postgres_handler.py
index a3456a8e95..40b756f39f 100644
--- a/mindsdb/integrations/handlers/postgres_handler/postgres_handler.py
+++ b/mindsdb/integrations/handlers/postgres_handler/postgres_handler.py
@@ -221,11 +221,19 @@ def connect(self):
             schema = self.connection_args.get("schema")
             if schema:
                 with self.connection.cursor() as cur:
+                    cur.execute("SELECT 1 FROM pg_namespace WHERE nspname = %s;", (schema,))
+                    if cur.fetchone() is None:
+                        raise psycopg.errors.InvalidSchemaName(
+                            f'Schema "{schema}" does not exist in database "{self.database}". '
+                            "Schema names are case-sensitive."
+                        )
                     cur.execute(f'SET search_path TO "{schema}", public;')
                 self.connection.commit()
             return self.connection
         except psycopg.Error as e:
             logger.error(f"Error connecting to PostgreSQL {self.database}, {e}!")
+            if self.is_connected:
+                self.connection.close()
             self.is_connected = False
             raise
 
diff --git a/tests/unit/handlers/test_postgres.py b/tests/unit/handlers/test_postgres.py
index a0e3adc133..4f74914078 100644
--- a/tests/unit/handlers/test_postgres.py
+++ b/tests/unit/handlers/test_postgres.py
@@ -294,9 +294,35 @@ def test_connect_with_schema_sets_search_path_after_connection(self):
         self.assertTrue(self.handler.is_connected)
         self.assertIsNotNone(connection)
 
-        mock_cursor.execute.assert_called_once_with('SET search_path TO "my_schema", public;')
+        mock_cursor.execute.assert_called_with('SET search_path TO "my_schema", public;')
         self.mock_connect.return_value.commit.assert_called_once()
 
+    def test_connect_with_missing_schema_fails(self):
+        """
+        Tests that a schema that does not exist (for example, wrong case) fails the connection
+        instead of silently falling back to the public schema.
+        """
+        self.tearDown()
+        self.setUp()
+        self.handler.connection_args["schema"] = "sales"
+
+        mock_cursor = MockCursorContextManager()
+        mock_cursor.fetchone = MagicMock(return_value=None)
+        mock_conn = self.mock_connect.return_value
+        mock_conn.cursor.return_value = mock_cursor
+
+        with self.assertRaises(psycopg.errors.InvalidSchemaName) as ctx:
+            self.handler.connect()
+
+        self.assertIn('Schema "sales" does not exist', str(ctx.exception))
+        mock_cursor.execute.assert_called_once_with("SELECT 1 FROM pg_namespace WHERE nspname = %s;", ("sales",))
+        self.assertFalse(self.handler.is_connected)
+        mock_conn.close.assert_called_once()
+
+        response = self.handler.check_connection()
+        self.assertFalse(response.success)
+        self.assertIn('Schema "sales" does not exist', response.error_message)
+
     def test_make_connection_args_applies_overrides(self):
         handler = self.handler
         handler.connection_args = OrderedDict(