feat: support deferred predicates in join

ibis/expr/operations/relations.py

@@ -13,6 +13,7 @@
 import ibis.expr.types as ir
 import ibis.util as util
 from ibis.common.annotations import attribute
+from ibis.expr.deferred import Deferred
 from ibis.expr.operations.core import Named, Node, Value
 from ibis.expr.operations.generic import TableColumn
 from ibis.expr.operations.logical import Equals, ExistsSubquery, NotExistsSubquery
@@ -109,6 +110,9 @@ def _clean_join_predicates(left, right, predicates):
             pred = left.to_expr()[pred] == right.to_expr()[pred]
         elif isinstance(pred, Value):
             pred = pred.to_expr()
+        elif isinstance(pred, Deferred):
+            # resolve deferred expressions on the left table
+            pred = pred.resolve(left.to_expr())
         elif not isinstance(pred, ir.Expr):
             raise NotImplementedError
 

ibis/tests/expr/test_table.py

@@ -794,6 +794,14 @@ def test_join_no_predicate_list(con):
     assert_equal(joined, expected)
 
 
+def test_join_deferred(con):
+    region = con.table("tpch_region")
+    nation = con.table("tpch_nation")
+    res = region.join(nation, _.r_regionkey == nation.n_regionkey)
+    exp = region.join(nation, region.r_regionkey == nation.n_regionkey)
+    assert_equal(res, exp)
+
+
 def test_asof_join():
     left = ibis.table([('time', 'int32'), ('value', 'double')])
     right = ibis.table([('time', 'int32'), ('value2', 'double')])