chore(clickhouse): add docs

ibis/backends/clickhouse/compiler.py

@@ -712,18 +712,26 @@ def visit_TableUnnest(
     def _cleanup_names(self, exprs: Mapping[str, sge.Expression]):
         """Compose `_gen_valid_name` and `_dedup_name` to clean up names in projections.
 
-        ClickHouse has a bug where this fails semantic validation, assuming `s`
-        has a column called `x`:
+        ClickHouse has a bug where this fails semantic validation:
 
         ```sql
-        SELECT t.x
-        FROM (SELECT * FROM s) t
+        SELECT
+          "o"."a"
+        FROM (
+          SELECT
+            "w"."a"
+          FROM "{name}" AS "s"
+          INNER JOIN "{name}" AS "w"
+          USING ("a")
+        ) AS "o"
         ```
 
-        so we need to add a redundant aliasing operation to columns
+        Adding a redundant aliasing operation here (`"w"."a" AS "a"`) helps
+        ClickHouse. Not entirely clear whether this is an upstream bug.
         """
 
         quoted = self.quoted
-        for name, value in exprs.items():
-            name = self._gen_valid_name(name)
-            yield value.as_(name, quoted=quoted, copy=False)
+        return (
+            value.as_(self._gen_valid_name(name), quoted=quoted, copy=False)
+            for name, value in exprs.items()
+        )

ibis/backends/clickhouse/tests/test_client.py

@@ -351,7 +351,7 @@ def test_create_table_no_syntax_error(con):
 
 
 def test_password_with_bracket():
-    password = f'{os.environ.get("IBIS_TEST_CLICKHOUSE_PASSWORD", "")}['
+    password = f'{os.environ.get("IBIS_TEST_CLICKHOUSE_PASSWORD", "")}[]'
     quoted_pass = quote_plus(password)
     host = os.environ.get("IBIS_TEST_CLICKHOUSE_HOST", "localhost")
     user = os.environ.get("IBIS_TEST_CLICKHOUSE_USER", "default")
@@ -365,25 +365,26 @@ def test_password_with_bracket():
 def test_subquery_with_join(con):
     name = gen_name("clickhouse_tmp_table")
 
-    con.create_table(name, ibis.memtable({"a": [1]}), temp=True)
+    s = con.create_table(name, pa.Table.from_pydict({"a": [1, 2, 3]}), temp=True)
 
     sql = f"""
-    WITH "t12" AS (
-      SELECT
-        "a"
-      FROM "{name}"
-    )
     SELECT
-      "t26"."a"
+      "o"."a"
     FROM (
       SELECT
-        "t23"."a"
-      FROM "t12" AS "t22"
-      INNER JOIN "t12" AS "t23"
+        "w"."a"
+      FROM "{name}" AS "s"
+      INNER JOIN "{name}" AS "w"
       USING ("a")
-    ) AS "t26"
+    ) AS "o"
     """
     with pytest.raises(
-        ClickHouseDatabaseError, match="Identifier 't26.a' cannot be resolved"
+        ClickHouseDatabaseError, match="Identifier 'o.a' cannot be resolved"
     ):
         con.sql(sql)
+
+    # this works because we add the additional alias in the inner query
+    w = s.view()
+    expr = s.join(w, "a").select(a=w.a).select(b=lambda t: t.a + 1)
+    result = expr.to_pandas()
+    assert set(result["b"].tolist()) == {2, 3, 4}