CROSS JOIN 多于两个表

Question

我有三个表，t1、t2 和 t3。 表结构和值：

t1_id | t1_k1 | t1_val
------+-------+--------
1     | k1foo | t1foo
2     | k1bar | t1bar
3     | k1baz | t1baz

t2_id | t2_k1 | t2_k2 | t2_val
------+-------+-------+--------
1     | k1foo | k2foo | t2foo
2     | k1bar | k2bar | t2bar
3     | k1baz | k2baz | t2baz

t3_id | t3_k2 | t3_val
------+-------+--------
1     | k2foo | t3foo
2     | k2bar | t3bar
3     | k2baz | t3baz

因此，对于正常的 SQL，我可以在 t1_k1 = t2_k1 上加入 t1 和 t2，在 t2_k2 = t3_k2 上加入 t2 和 t3，即：

SELECT t1_val, t2_val, t3_val
FROM t1, t2, t3
WHERE t1_k1 = t2_k1 AND t2_k2 = t3_k2

要得到

t1foo | t2foo | t3foo
t1bar | t2bar | t3bar
t1baz | t2baz | t3baz

现在我尝试使用 bigQuery SQL 获得相同的结果。 据我了解，使用 CROSS JOIN 应该像常规 SQL 中的逗号一样工作，所以我认为以下方法可以工作：

SELECT t1_val, t2_val, t3_val
FROM test.t1 CROSS JOIN test.t2 CROSS JOIN test.t3
WHERE t1_k1 = t2_k1 AND t2_k2 = t3_k2

但我收到一个错误，“在 JOIN 的任何一侧都找不到字段 't3_k2'”。 像这样添加括号：

SELECT SELECT t1_val, t2_val, t3_val
FROM ((test.t1 CROSS JOIN test.t2) CROSS JOIN test.t3)
WHERE t1_k1 = t2_k1 AND t2_k2 = t3_k2

给出一个（坦率地说非常神秘的）语法错误“在第 0 行第 0 列遇到“”。 只有两个表 CROSS JOIN 可以工作，但它与普通的 JOIN 没有什么不同。 我还没有找到在两个以上的表上使用 CROSS JOIN 的示例。 可能吗？ 难道我做错了什么？

Answer 1

试试下面

SELECT t1_val, t2_val, t3_val 
FROM (
  SELECT t1_val, t2_val, t2_k2
  FROM test.t1 AS a 
  CROSS JOIN test.t2 AS b
  WHERE t1_k1 = t2_k1 
) AS c
CROSS JOIN test.t3 AS d
WHERE t2_k2 = t3_k2

注意：我认为您的示例仅用于解决CROSS JOIN问题-但要提及的是，如果您的示例确实代表您的问题-您不需要CROSS JOIN-而是需要[INNER] JOIN，如下所示

SELECT t1_val, t2_val, t3_val
FROM (
  SELECT t1_val, t2_val, t2_k2
  FROM test.t1 AS a JOIN test.t2 AS b
  ON t1_k1 = t2_k1 
) AS c
JOIN test.t3 AS d ON t2_k2 = t3_k2

添加了第二个查询的可运行示例-证明它有效：o）

SELECT t1_val, t2_val, t3_val
FROM (
  SELECT t1_val, t2_val, t2_k2
  FROM (
    SELECT * FROM 
    (SELECT 1 AS t1_id, 'k1foo' AS t1_k1, 't1foo' AS t1_val),
    (SELECT 2 AS t1_id, 'k1bar' AS t1_k1, 't1bar' AS t1_val),
    (SELECT 3 AS t1_id, 'k1baz' AS t1_k1, 't1baz' AS t1_val)
  ) AS a 
  JOIN (
    SELECT * FROM 
    (SELECT 1 AS t2_id, 'k1foo' AS t2_k1, 'k2foo' AS t2_k2, 't2foo' AS t2_val),
    (SELECT 2 AS t2_id, 'k1bar' AS t2_k1, 'k2bar' AS t2_k2, 't2bar' AS t2_val),
    (SELECT 3 AS t2_id, 'k1baz' AS t2_k1, 'k2baz' AS t2_k2, 't2baz' AS t2_val)
  ) AS b
  ON t1_k1 = t2_k1 
) as c
JOIN (
  SELECT * FROM 
  (SELECT 1 AS t3_id, 'k2foo' AS t3_k2, 't3foo' AS t3_val),
  (SELECT 2 AS t3_id, 'k2bar' AS t3_k2, 't3bar' AS t3_val),
  (SELECT 3 AS t3_id, 'k2baz' AS t3_k2, 't3baz' AS t3_val)
) AS d
ON t2_k2 = t3_k2

Answer 2

正如Mikhail在他的回答中注意到的那样，您不需要CROSS JOIN，常规JOIN可以正常工作。 这是在没有多级JOIN的情况下用一条语句执行的方法：

我使用内联SELECT语句为t1，t2，t3提供数据：

SELECT t1_val, t2_val, t3.t3_val as t3_val
FROM (SELECT 1 as t1_id, "k1foo" as t1_k1, "t1foo" as t1_val) t1
JOIN (SELECT 1 as t2_id, "k1foo" as t2_k1, "k2foo" as t2_k2, "t2foo" as t2_val) t2
ON t1_k1 = t2_k1 
JOIN (SELECT 1 as t3_id, "k2foo" as t3_k2, "t3foo" as t3_val) t3
ON t2_k2 = t3_k2

Answer 3

所以事实证明，这完全是定义表别名的问题，请参见另一个问题的示例： CROSS JOIN：只有两个表？ 。

Answer 4

也许它在过去 6 年发生了变化，但现在使用逗号作为 CROSS JOIN 作品，你只需要小心歧义。

SELECT 
  t1_val, 
  t2_val, 
  t3_val
FROM (
  SELECT * FROM 
  (SELECT 1 AS t1_id, 'k1foo' AS t1_k1, 't1foo' AS t1_val) UNION ALL
  (SELECT 2 AS t1_id, 'k1bar' AS t1_k1, 't1bar' AS t1_val) UNION ALL
  (SELECT 3 AS t1_id, 'k1baz' AS t1_k1, 't1baz' AS t1_val)
) AS a
,(
  SELECT * FROM 
  (SELECT 1 AS t2_id, 'k1foo' AS t2_k1, 'k2foo' AS t2_k2, 't2foo' AS t2_val) UNION ALL
  (SELECT 2 AS t2_id, 'k1bar' AS t2_k1, 'k2bar' AS t2_k2, 't2bar' AS t2_val) UNION ALL
  (SELECT 3 AS t2_id, 'k1baz' AS t2_k1, 'k2baz' AS t2_k2, 't2baz' AS t2_val)
) AS b
,(
  SELECT * FROM 
  (SELECT 1 AS t3_id, 'k2foo' AS t3_k2, 't3foo' AS t3_val) UNION ALL
  (SELECT 2 AS t3_id, 'k2bar' AS t3_k2, 't3bar' AS t3_val) UNION ALL
  (SELECT 3 AS t3_id, 'k2baz' AS t3_k2, 't3baz' AS t3_val)
) AS c
where
  a.t1_k1 = b.t2_k1 
  AND b.t2_k2 = c.t3_k2

上面的查询结果：

t1foo | t2foo | t3foo
t1bar | t2bar | t3bar
t1baz | t2baz | t3baz

您可以复制并粘贴以检查。

---

但是，是的，在这个具体的例子中，正如 Michael 和 Mikhail 指出的那样，使用 INNER JOIN 会更好。