fix: allow inserting memtable with alchemy backends

Now if a user passes a `memtable` to `insert` we'll pull out the
underlying dataframe and use that to update the table.

ibis/backends/base/sql/alchemy/__init__.py

@@ -473,6 +473,12 @@ def insert(
                 'yet implemented'
             )
 
+        # If we've been passed a `memtable`, pull out the underlying dataframe
+        if isinstance(obj, ir.Table) and isinstance(
+            in_mem_table := obj.op(), ops.InMemoryTable
+        ):
+            obj = in_mem_table.data.to_frame()
+
         if isinstance(obj, pd.DataFrame):
             obj.to_sql(
                 table_name,

ibis/backends/tests/test_client.py

@@ -349,6 +349,21 @@ def _emp(a, b, c, d):
     assert len(alchemy_con.table(employee_data_1_temp_table).execute()) == 3
 
 
+def test_insert_from_memtable(alchemy_con):
+    df = pd.DataFrame({"x": range(3)})
+    table_name = "memtable_test"
+    alchemy_con.insert(table_name, ibis.memtable(df))
+    alchemy_con.insert(table_name, ibis.memtable(df))
+
+    try:
+        table = alchemy_con.tables[table_name]
+        assert len(table.execute()) == 6
+        assert alchemy_con.tables[table_name].schema() == ibis.schema({"x": "int64"})
+    finally:
+        alchemy_con.raw_sql(f"DROP TABLE IF EXISTS {table_name}")
+        assert table_name not in alchemy_con.list_tables()
+
+
 def test_list_databases(alchemy_con):
     # Every backend has its own databases
     TEST_DATABASES = {