Make meta consistent with results of cross join (#300)

* Drop temp join column for single partition case

* Adjust cross join meta instead of partitions

dask_sql/physical/rel/logical/join.py

@@ -140,7 +140,11 @@ def merge_single_partitions(lhs_partition, rhs_partition):
             )
 
             meta = dd.dispatch.concat(
-                [df_lhs_renamed._meta_nonempty, df_rhs_renamed._meta_nonempty], axis=1
+                [
+                    df_lhs_renamed._meta_nonempty.assign(common=1),
+                    df_rhs_renamed._meta_nonempty,
+                ],
+                axis=1,
             )
             # TODO: Do we know the divisions in any way here?
             divisions = [None] * (len(dsk) + 1)

tests/integration/test_compatibility.py

@@ -239,7 +239,15 @@ def test_join_left():
 def test_join_cross():
     a = make_rand_df(10, a=(int, 4), b=(str, 4), c=(float, 4))
     b = make_rand_df(20, dd=(float, 1), aa=(int, 1), bb=(str, 1))
-    eq_sqlite("SELECT * FROM a CROSS JOIN b", a=a, b=b)
+    eq_sqlite(
+        """
+        SELECT * FROM a
+            CROSS JOIN b
+        ORDER BY a.a NULLS FIRST, a.b NULLS FIRST, a.c NULLS FIRST, dd NULLS FIRST
+        """,
+        a=a,
+        b=b,
+    )
 
 
 def test_join_multi():