simplify SQL query a bit

With SQLite it's in general not a big issue to run multiple smaller
queries instead a big one, because the overhead per request is much
smaller than with separate DBMS.
This should make it easier to extend `find_ratings` in the future.

unwind/db.py

@@ -456,43 +456,39 @@ async def find_ratings(
         values.update(uvs)
         user_condition = f"{Rating._table}.user_id IN ({','.join(':'+n for n in uvs)})"
 
-    source_table = "newest_movies"
-    ctes = [
-        f"""{source_table} AS (
+    query = f"""
         SELECT DISTINCT {Rating._table}.movie_id
         FROM {Rating._table}
         LEFT JOIN {Movie._table} ON {Movie._table}.id={Rating._table}.movie_id
         WHERE {user_condition}{(' AND ' + ' AND '.join(conditions)) if conditions else ''}
         ORDER BY length({Movie._table}.title) ASC, {Rating._table}.rating_date DESC, {Movie._table}.imdb_score DESC
         LIMIT :limit_rows
-        )"""
-    ]
+    """
+    async with locked_connection() as conn:
+        rows = await conn.fetch_all(bindparams(query, values))
+        movie_ids = tuple(r["movie_id"] for r in rows)
 
-    if include_unrated:
-        source_table = "target_movies"
-        ctes.extend(
-            [
-                f"""unrated_movies AS (
+    if include_unrated and len(movie_ids) < limit_rows:
+        sqlin, sqlin_vals = sql_in("id", movie_ids, not_=True)
+        query = f"""
             SELECT DISTINCT id AS movie_id
             FROM {Movie._table}
-                    WHERE id NOT IN newest_movies
+            WHERE {sqlin}
             {('AND ' + ' AND '.join(conditions)) if conditions else ''}
             ORDER BY length(title) ASC, imdb_score DESC, release_year DESC
             LIMIT :limit_rows
-                )""",
-                f"""{source_table} AS (
-                    SELECT * FROM newest_movies
-                    UNION ALL  -- using ALL here avoids the reordering of IDs
-                    SELECT * FROM unrated_movies
-                    LIMIT :limit_rows
-                )""",
-            ]
+        """
+        async with locked_connection() as conn:
+            rows = await conn.fetch_all(
+                bindparams(
+                    query,
+                    {**values, **sqlin_vals, "limit_rows": limit_rows - len(movie_ids)},
                 )
+            )
+            movie_ids += tuple(r["movie_id"] for r in rows)
 
+    sqlin, sqlin_vals = sql_in(f"{Movie._table}.id", movie_ids)
     query = f"""
-        WITH
-            {','.join(ctes)}
-
         SELECT 
             {Rating._table}.score AS user_score,
             {Rating._table}.user_id AS user_id,
@@ -503,13 +499,13 @@ async def find_ratings(
             {Movie._table}.title AS canonical_title,
             {Movie._table}.original_title AS original_title,
             {Movie._table}.release_year AS release_year
-        FROM {source_table}
-        LEFT JOIN {Rating._table} ON {Rating._table}.movie_id={source_table}.movie_id
-        LEFT JOIN {Movie._table} ON {Movie._table}.id={source_table}.movie_id
+        FROM {Movie._table}
+        LEFT JOIN {Rating._table} ON {Movie._table}.id={Rating._table}.movie_id
+        WHERE {sqlin}
     """
 
     async with locked_connection() as conn:
-        rows = await conn.fetch_all(bindparams(query, values))
+        rows = await conn.fetch_all(bindparams(query, {**values, **sqlin_vals}))
     return tuple(dict(r) for r in rows)
 
 
@@ -533,10 +529,12 @@ def demux(tp: Type[ModelType], row) -> ModelType:
     return fromplain(tp, d, serialized=True)
 
 
-def sql_in(column: str, values: list[T]) -> tuple[str, dict[str, T]]:
+def sql_in(column: str, values: Iterable[T], not_=False) -> tuple[str, dict[str, T]]:
     c = column.replace(".", "___")
     value_map = {f"{c}_{i}": v for i, v in enumerate(values, start=1)}
     placeholders = ",".join(":" + k for k in value_map)
+    if not_:
+        return f"{column} NOT IN ({placeholders})", value_map
     return f"{column} IN ({placeholders})", value_map