fix(clickhouse): make sure that array1.union(array2) null handling …

…matches across backends

ibis/backends/clickhouse/compiler/values.py

@@ -1092,7 +1092,6 @@ def formatter(op, **kw):
     ops.BitwiseLeftShift: "bitShiftLeft",
     ops.BitwiseRightShift: "bitShiftRight",
     ops.BitwiseNot: "bitNot",
-    ops.ArrayDistinct: "arrayDistinct",
     ops.ArraySort: "arraySort",
     ops.ArrayContains: "has",
     ops.FirstValue: "first_value",
@@ -1116,6 +1115,13 @@ def _fmt(op, _name: str = _name, **kw):
 del _fmt, _name, _op
 
 
+@translate_val.register(ops.ArrayDistinct)
+def _array_distinct(op, **kw):
+    arg = translate_val(op.arg, **kw)
+    null_element = f"if(countEqual({arg}, NULL) > 0, [NULL], [])"
+    return f"arrayConcat(arrayDistinct({arg}), {null_element})"
+
+
 @translate_val.register(ops.ExtractMicrosecond)
 def _extract_microsecond(op, **kw):
     arg = translate_val(op.arg, **kw)

ibis/backends/tests/test_array.py

@@ -617,6 +617,11 @@ def test_array_remove(backend, con):
     raises=com.IbisTypeError,
     reason="argument passes none of the following rules:....",
 )
+@pytest.mark.notyet(
+    ["clickhouse"],
+    raises=TypeError,
+    reason="clickhouse doesn't support nullable array types",
+)
 def test_array_unique(backend, con):
     t = ibis.memtable({"a": [[1, 3, 3], [], [42, 42], [], [None], None]})
     expr = t.a.unique()