feat(api): add positional joins (#9533)

Co-authored-by: Phillip Cloud <417981+cpcloud@users.noreply.github.com>

ibis/backends/pandas/executor.py

@@ -642,6 +642,9 @@ def visit(cls, op: PandasJoin, how, left, right, left_on, right_on):
         if how == "cross":
             assert not left_on and not right_on
             return cls.merge(left, right, how="cross")
+        elif how == "positional":
+            assert not left_on and not right_on
+            return cls.concat([left, right], axis=1)
         elif how == "anti":
             df = cls.merge(
                 left,

ibis/backends/polars/compiler.py

@@ -296,6 +296,9 @@ def join(op, **kw):
     left = translate(op.left, **kw)
     right = translate(op.right, **kw)
 
+    if how == "positional":
+        return pl.concat([left, right], how="horizontal")
+
     # workaround required for https://github.com/pola-rs/polars/issues/13130
     prefix = gen_name("on")
     left_on = {f"{prefix}_{i}": translate(v, **kw) for i, v in enumerate(op.left_on)}

ibis/backends/sql/compilers/base.py

@@ -1259,6 +1259,7 @@ def visit_JoinLink(self, op, *, how, table, predicates):
             "asof": "asof",
             "any_left": "left",
             "any_inner": None,
+            "positional": None,
         }
         kinds = {
             "any_left": "any",
@@ -1271,11 +1272,12 @@ def visit_JoinLink(self, op, *, how, table, predicates):
             "anti": "anti",
             "cross": "cross",
             "outer": "outer",
+            "positional": "positional",
         }
-        assert (
-            predicates or how == "cross"
-        ), "expected non-empty predicates when not a cross join"
-
+        assert predicates or how in {
+            "cross",
+            "positional",
+        }, "expected non-empty predicates when not a cross join"
         on = sg.and_(*predicates) if predicates else None
         return sge.Join(this=table, side=sides[how], kind=kinds[how], on=on)
 

ibis/backends/tests/test_join.py

@@ -385,3 +385,33 @@ def test_join_conflicting_columns(backend, con):
         }
     )
     backend.assert_frame_equal(result, expected)
+
+
+@pytest.mark.never(
+    [
+        "bigquery",
+        "clickhouse",
+        "datafusion",
+        "druid",
+        "exasol",
+        "flink",
+        "impala",
+        "mssql",
+        "mysql",
+        "oracle",
+        "postgres",
+        "pyspark",
+        "risingwave",
+        "snowflake",
+        "sqlite",
+        "trino",
+    ],
+    reason="Users can implement this with ibis.row_number(): https://github.com/ibis-project/ibis/issues/9486",
+)
+def test_positional_join(backend, con):
+    t1 = ibis.memtable({"x": [1, 2, 3]})
+    t2 = ibis.memtable({"x": [3, 2, 1]})
+    j = t1.join(t2, how="positional")
+    result = con.execute(j)
+    expected = pd.DataFrame({"x": [1, 2, 3], "x_right": [3, 2, 1]})
+    backend.assert_frame_equal(result, expected)

ibis/expr/operations/relations.py

@@ -205,6 +205,7 @@ def values(self):
     "any_inner",
     "any_left",
     "cross",
+    "positional",
 ]
 
 

ibis/expr/types/joins.py

@@ -269,7 +269,7 @@ def join(
         # bind and dereference the predicates
         preds = prepare_predicates(chain, right, predicates)
         preds = flatten_predicates(preds)
-        if not preds and how != "cross":
+        if not preds and how not in {"cross", "positional"}:
             # if there are no predicates, default to every row matching unless
             # the join is a cross join, because a cross join already has this
             # behavior