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，使用普通 SQL，我可以在 t1_k1 = t2_k1 上连接 t1 和 t2，在 t2_k2 = t3_k2 上连接 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
获取
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。根据我的理解，使用 CROSS JOIN 应该像常规 SQL 中的逗号一样工作，所以我认为以下内容可以工作：
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
但是我收到错误“在 JOIN 的任一侧都找不到字段 '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（坦率地说相当神秘的）语法错误“在第 0 行第 0 列遇到“”。” 只需两个表，CROSS JOIN 就可以工作，但它与普通 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。是否可以？我是不是做错了什么？
尝试以下
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：我认为您的示例只是为了解决您的 CROSS JOIN 问题而定制的 - 但想提一下，如果您的示例确实代表了您的问题 - 您不需要 CROSS JOIN - 相反，您需要 [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
为第二个查询添加了可运行示例 - 以证明它有效: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
正如 Mikhail 在他的回答中注意到的那样，你不需要 CROSS JOIN，常规 JOIN 就可以了。以下是如何在一条语句中完成此操作，无需多级 JOIN：
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
所以事实证明这都是定义表别名的问题，请参阅另一个问题的示例：CROSS JOIN：只有两个表？.
也许在过去的6年里它发生了变化，但现在使用逗号作为CROSS JOIN的作品，你只需要小心歧义即可。
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
以上查询结果为：
t1foo | t2foo | t3foo
t1bar | t2bar | t3bar
t1baz | t2baz | t3baz
您可以复制粘贴来查看。
但是，是的，在这个具体示例中，最好使用 Michael 和 Mikhail 指出的 INNER JOIN。
我自己也遇到了这个问题，并通过执行以下操作非常简单地解决了它：
SELECT
shirts.shirt_color,
pants.pants_color,
socks.sock_color
FROM
shirts
CROSS JOIN pants
CROSS JOIN socks;
这些似乎对我在 BQ 有用
来源：https://discuss.codecademy.com/t/can-you-cross-join-on-more-than-two-tables/356104