我有 2 个 sql 数据集:
数据集 1:
select * from (
Select 1 rn, 'b' c, 3 Val from dual UNION ALL
Select 1 rn, 'r' c, 3 Val from dual UNION ALL
Select 1 rn, 'w' c, 3 Val from dual UNION ALL
Select 2 rn, 'b' c, 2 Val from dual UNION ALL
Select 2 rn, 'r' c, 2 Val from dual UNION ALL
Select 3 rn, 'b' c, 1 Val from dual
) t1
数据集 2:
select * from (
Select 'b' c from dual UNION ALL
Select 'r' c from dual UNION ALL
Select 'w' c from dual ) t2
我需要获取以下数据集:
rn c val
1 b 3
1 r 3
1 w 3
2 b 2
2 r 2
2 w null
3 b 1
3 r null
3 w null
我尝试使用以下 sql 执行此操作,但它不起作用。
select t1.*, t2.*
FROM (
Select 1 rn, 'b' c, 3 Val from dual UNION ALL
Select 1 rn, 'r' c, 3 Val from dual UNION ALL
Select 1 rn, 'w' c, 3 Val from dual UNION ALL
Select 2 rn, 'b' c, 2 Val from dual UNION ALL
Select 2 rn, 'r' c, 2 Val from dual UNION ALL
Select 3 rn, 'b' c, 1 Val from dual
) t1 right join (
Select 'b' c from dual UNION ALL
Select 'r' c from dual UNION ALL
Select 'w' c from dual ) t2 on t1.c=t2.c
order by 1,2
请帮我解决我的问题。我使用 Oracle 数据库。
最佳答案
这是分区外连接的确切用例。对于大型数据集,它应该比 CROSS JOIN
方法更有效。
语法是这样的:
select t1.rn,
t2.c,
t1.val
from t1 partition by (rn) right join t2 on t2.c = t1.c;
PARTITION BY
关键字告诉 Oracle 为 t1.rn
的每个不同值重复外部连接。
这是一个完整的例子:
with t1 as (
Select 1 rn, 'b' c, 3 Val from dual UNION ALL
Select 1 rn, 'r' c, 3 Val from dual UNION ALL
Select 1 rn, 'w' c, 3 Val from dual UNION ALL
Select 2 rn, 'b' c, 2 Val from dual UNION ALL
Select 2 rn, 'r' c, 2 Val from dual UNION ALL
Select 3 rn, 'b' c, 1 Val from dual
),
t2 as (
Select 'b' c from dual UNION ALL
Select 'r' c from dual UNION ALL
Select 'w' c from dual
)
select t1.rn,
t2.c,
t1.val
from t1 partition by (rn) right join t2 on t2.c = t1.c;
+----+---+-----+ | RN | C | VAL | +----+---+-----+ | 1 | b | 3 | | 1 | r | 3 | | 1 | w | 3 | | 2 | b | 2 | | 2 | r | 2 | | 2 | w | - | | 3 | b | 1 | | 3 | r | - | | 3 | w | - | +----+---+-----+
关于sql - 困难连接 (SQL),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/70571771/