CROSS JOIN超過兩個表

Question

我有三個表，t1，t2和t3。表結構和值：

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，與普通的SQL我可以加入t1和t2上t1_k1 = t2_k1和T2和T3上t2_k2 = t3_k2，那就是：

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

要獲得

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

現在我試圖用bigQuery SQL得到相同的結果。從我的理解，使用CROSS JOIN應該工作就像普通的SQL逗號，所以我想下面將工作：

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 

但我得到一個錯誤，「場‘t3_k2’上的任何一方未找到加入」。 添加括號這樣的：

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 

給出了一個（相當坦率隱蔽）的語法錯誤「遇到‘’在線0，列0」。 只有兩個表CROSS JOIN可以工作，但與正常的JOIN沒有區別。 我還沒有發現在兩個以上的表上使用CROSS JOIN的例子。可能嗎？難道我做錯了什麼？

Answer 1

嘗試以下

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：我認爲你的例子只是針對解決您的CROSS JOIN的問題 - 但想提一提，如果你的榜樣真正代表您的問題 - 你不需要CROSS JOIN - 而你需要[INNER] JOIN，如下

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 

對於第二個查詢增加可運行的例子 - 來證明它的工作原理：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

由於米哈伊爾在他的回答中注意到，你不需要CROSS JOIN，常規的JOIN工作正常。以下是如何做到這一點在一個聲明中，沒有多層次的連接：

我用內嵌SELECT語句，以提供T1，T2，T3數據：

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

因此，原來它的定義是所有問題表別名，請參閱其他問題的例子：CROSS JOIN: only two tables?。