-- Migrated from DuckDB test: test/sql/join/ NULL handling tests
-- Tests join behavior with NULL values
CREATE TABLE table_with_nulls("id" INTEGER, "value" VARCHAR, "category" INTEGER, ts TIMESTAMP TIME INDEX);

Affected Rows: 0

CREATE TABLE lookup_table("category" INTEGER, cat_name VARCHAR, priority INTEGER, ts TIMESTAMP TIME INDEX);

Affected Rows: 0

INSERT INTO table_with_nulls VALUES
(1, 'item1', 1, 1000), (2, 'item2', NULL, 2000), (3, 'item3', 2, 3000),
(4, 'item4', NULL, 4000), (5, 'item5', 3, 5000), (6, 'item6', 1, 6000);

Affected Rows: 6

INSERT INTO lookup_table VALUES
(1, 'Category A', 1, 1000), (2, 'Category B', 2, 2000), (3, 'Category C', 3, 3000), (NULL, 'Unknown', 0, 4000);

Affected Rows: 4

-- Inner join with NULLs (NULLs won't match)
SELECT t."id", t."value", l.cat_name
FROM table_with_nulls t
INNER JOIN lookup_table l ON t.category = l.category
ORDER BY t."id";

+----+-------+------------+
| id | value | cat_name   |
+----+-------+------------+
| 1  | item1 | Category A |
| 3  | item3 | Category B |
| 5  | item5 | Category C |
| 6  | item6 | Category A |
+----+-------+------------+

-- Left join with NULLs
SELECT t."id", t."value", t.category, COALESCE(l.cat_name, 'No Category') as category_name
FROM table_with_nulls t
LEFT JOIN lookup_table l ON t.category = l.category
ORDER BY t."id";

+----+-------+----------+---------------+
| id | value | category | category_name |
+----+-------+----------+---------------+
| 1  | item1 | 1        | Category A    |
| 2  | item2 |          | No Category   |
| 3  | item3 | 2        | Category B    |
| 4  | item4 |          | No Category   |
| 5  | item5 | 3        | Category C    |
| 6  | item6 | 1        | Category A    |
+----+-------+----------+---------------+

-- Join with explicit NULL handling
SELECT
  t."id", t."value",
  CASE
    WHEN t.category IS NULL THEN 'NULL Category'
    WHEN l.cat_name IS NULL THEN 'Missing Lookup'
    ELSE l.cat_name
  END as resolved_category
FROM table_with_nulls t
LEFT JOIN lookup_table l ON t.category = l.category
ORDER BY t."id";

+----+-------+-------------------+
| id | value | resolved_category |
+----+-------+-------------------+
| 1  | item1 | Category A        |
| 2  | item2 | NULL Category     |
| 3  | item3 | Category B        |
| 4  | item4 | NULL Category     |
| 5  | item5 | Category C        |
| 6  | item6 | Category A        |
+----+-------+-------------------+

-- NULL-safe join using COALESCE
SELECT t."id", t."value", l.cat_name
FROM table_with_nulls t
INNER JOIN lookup_table l ON COALESCE(t.category, -1) = COALESCE(l.category, -1)
ORDER BY t."id";

+----+-------+------------+
| id | value | cat_name   |
+----+-------+------------+
| 1  | item1 | Category A |
| 2  | item2 | Unknown    |
| 3  | item3 | Category B |
| 4  | item4 | Unknown    |
| 5  | item5 | Category C |
| 6  | item6 | Category A |
+----+-------+------------+

-- Aggregation with NULL join results
SELECT
  COALESCE(l.cat_name, 'Uncategorized') as category,
  COUNT(*) as item_count,
  COUNT(l.category) as matched_count,
  COUNT(*) - COUNT(l.category) as unmatched_count
FROM table_with_nulls t
LEFT JOIN lookup_table l ON t.category = l.category
GROUP BY l.cat_name
ORDER BY item_count DESC, category DESC;

+---------------+------------+---------------+-----------------+
| category      | item_count | matched_count | unmatched_count |
+---------------+------------+---------------+-----------------+
| Uncategorized | 2          | 0             | 2               |
| Category A    | 2          | 2             | 0               |
| Category C    | 1          | 1             | 0               |
| Category B    | 1          | 1             | 0               |
+---------------+------------+---------------+-----------------+

DROP TABLE table_with_nulls;

Affected Rows: 0

DROP TABLE lookup_table;

Affected Rows: 0

