feat(api): add TableUnnest operation to support cross-join unnest s…

…emantics as well as `offset`

ibis/backends/sql/compiler.py

@@ -1512,6 +1512,23 @@ def visit_Unsupported(self, op, **_):
             f"{type(op).__name__!r} operation is not supported in the {self.dialect} backend"
         )
 
+    def visit_TableUnnest(self, op, *, parent, column, offset: str | None):
+        quoted = self.quoted
+        columns = [
+            sg.column(k, parent.alias_or_name, quoted=quoted)
+            for k in op.parent.schema.keys()
+        ]
+        if offset is not None:
+            offset = sg.to_identifier(offset, quoted=quoted)
+            columns.append(offset)
+        column_alias = sg.to_identifier(op.column.name, quoted=self.quoted)
+        expr = sg.select(*columns, column_alias)
+        alias = sge.TableAlias(columns=[column_alias])
+        return expr.from_(parent).join(
+            sge.Unnest(expressions=[column], alias=alias, offset=offset),
+            how="CROSS",
+        )
+
 
 # `__init_subclass__` is uncalled for subclasses - we manually call it here to
 # autogenerate the base class implementations as well.

ibis/backends/tests/test_array.py

@@ -1388,3 +1388,10 @@ def test_zip_unnest_lift(con):
     result = con.execute(lifted)
     expected = pd.DataFrame({"f1": [1, 2, 3], "f2": [4, 5, 6]})
     tm.assert_frame_equal(result, expected)
+
+
+def test_table_unnest(backend):
+    t = backend.array_types
+    expr = t.unnest(t.x.name("unnested_x"), offset="i")
+    result = expr.execute()
+    assert len(result)

ibis/expr/operations/relations.py

@@ -468,4 +468,22 @@ class Distinct(Simple):
     """Compute the distinct rows of a table."""
 
 
+@public
+class TableUnnest(Simple):
+    """Cross join unnest operation."""
+
+    column: Value[dt.Array]
+    offset: typing.Union[str, None]
+
+    @attribute
+    def schema(self):
+        column = self.column
+        offset = self.offset
+
+        base = self.parent.schema | Schema({column.name: column.dtype.value_type})
+        if offset is not None:
+            base |= Schema({offset: dt.int64})
+        return base
+
+
 # TODO(kszucs): support t.select(*t) syntax by implementing Table.__iter__()

ibis/expr/types/relations.py

@@ -4677,6 +4677,13 @@ def value_counts(self) -> ir.Table:
             lambda t: t.count().name("_".join(columns) + "_count")
         )
 
+    def unnest(self, column, offset: str | None = None) -> Table:
+        """Unnest an array `column` from a table.
+
+        Optionally include `offset` for enumerating array indices.
+        """
+        return ops.TableUnnest(parent=self, column=column, offset=offset).to_expr()
+
 
 @public
 class CachedTable(Table):