組合的唯一值列中的一列

Question

我需要在表中的列中找到所有唯一可能的值組合。例如，對於列值1,2,3,4,5。我想要的結果是[1,2]，[1,3]，[1,4]，[1,5]，[2,1]，[2,3]等

指針構造查詢以查找值的組合。

感謝

Answer 1

一個cross join可能是有用的。

看到這個演示：http://www.sqlfiddle.com/#!12/59af5/1

的ANSI SQL語法使用CROSS JOIN操作：

create table val(x int); 
insert into val values(1),(2),(3),(4),(5); 

SELECT a.x a, b.x b 
FROM val a 
CROSS JOIN val b 
WHERE a.x <> b.x 
ORDER BY a,b; 

沒有CROSS JOIN應該大多數DBMS系統上運行該查詢的另一種形式，但建議ANSI形式清晰度：

SELECT a.x a, b.x b 
FROM val a, val b 
WHERE a.x <> b.x 
ORDER BY a,b; 

請注意，大數據集的交叉連接可能會導致數據庫性能下降，對於100個值，它會生成100x100 = 10.000行，對於1000 - > 1.000.000行。

Answer 2

您可以通過使用添加常量鍵值的子查詢來在BigQuery中進行交叉連接，然後加入該常量值。

例如，這裏是一個查詢，將計算的交叉聯接{1，2，3}和{2，4,6}：

SELECT t1.num as first, t2.num as second 
FROM (
    SELECT num, 1 as key 
    FROM (
     SELECT 1 as num), (
     SELECT 2 as num), (
     SELECT 3 as num)) as t1 
JOIN (
    SELECT num, 1 as key 
    FROM (
     SELECT 2 as num), (
     SELECT 4 as num), (
     SELECT 6 as num)) as t2 
ON t1.key = t2.key 
WHERE t1.num <> t2.num 

注意此使用大量查詢 「特技」，以創建兩個輸入表。如果你只是用現有的表做這件事，它看起來像：

SELECT t1.num as first, t2.num as second 
FROM (
    SELECT foo as num, 1 as key 
    FROM [my_dataset.my_table]) as t1 
JOIN (
    SELECT foo as num, 1 as key 
    FROM [my_dataset.my_table]) as t2 
ON t1.key = t2.key 
WHERE t1.num <> t2.num