test(sql): add xfails for backends when cross-database load fails with overwrite

Author: Andrew Ardill

ibis/backends/tests/test_client.py

@@ -1855,7 +1855,21 @@ def test_table_not_found(con):
         con.table(gen_name("table_not_found"))
 
 
-@pytest.mark.parametrize("overwrite", [True, False])
+@pytest.mark.parametrize(
+    "overwrite",
+    [
+        param(
+            True,
+            marks=[
+                pytest.mark.notimpl(
+                    ["mysql", "singlestoredb", "risingwave"],
+                    reason="Cross-database load fails with overwrite (needs investigation).",
+                )
+            ],
+        ),
+        False,
+    ],
+)
 @pytest.mark.notimpl(
     ["flink"], raises=com.IbisError, reason="not yet implemented for Flink"
 )