汇总基于一个共同的列值从同一个表中唯一的一对列值的

Question

我有如下表：

my_table 
------------------------ 
| common_id | uniq_val | 
------------------------ 
| 1  | foo |   
------------------------ 
| 1  | bar |   
------------------------ 

我想总价值从它使得生成的查询看起来像：

DESIRED RESULT 
--------------------------------------- 
| common_id | uniq_val_1 | uniq_val_2 | 
--------------------------------------- 
| 1  |  foo |  bar | 
--------------------------------------- 

OR 

--------------------------------------- 
| common_id | uniq_val_1 | uniq_val_2 | 
--------------------------------------- 
| 1  |  bar |  foo | 
--------------------------------------- 

所以我写查询：

SELECT t1.common_id, t1.uniq_val, t2.uniq_val 
FROM my_table t1 JOIN my_table AS t2 
ON t1.common_id=t2.common_id 
WHERE t1.uniq_val!=t2.uniq_val; 

导致

RESULTING SELECT 
--------------------------------------- 
| common_id | uniq_val_1 | uniq_val_2 | 
--------------------------------------- 
| 1  |  foo |  foo | 
--------------------------------------- 
| 1  |  bar |  bar | 
--------------------------------------- 

但我只需要这些列中的一个，所以我应该能够做一个GROUP BY t1.common_id，如：

SELECT t1.common_id, t1.uniq_val, t2.uniq_val 
FROM my_table t1 JOIN my_table AS t2 
ON t1.common_id=t2.common_id 
WHERE t1.uniq_val!=t2.uniq_val 
GROUP BY t1.common_id; 

不幸的是这将返回错误：

ERROR: column "t1.uniq_val" must appear in the GROUP BY clause or be used in an aggregate function 

任何人都可以指出我的逻辑错误吗？

Answer 1

简单聚合怎么样？

select common_id, min(uniq_val) as uniq_val_1, max(uniq_val) as uniq_val_2 
from my_table 
group by common_id; 

Answer 2

你可以尝试distinct on

SELECT distinct on (t1.common_id) t1.common_id, t1.uniq_val, t2.uniq_val FROM my_table t1 JOIN my_table AS t2 ON t1.common_id=t2.common_id WHERE t1.uniq_val!=t2.uniq_val;

我认为它会产生你所需要的！

Answer 3

这将处理每个common_id最多10个uniq_val值。如果需要，您可以删除或添加更少或更多的uniq_val值。

在这里看到一个示范与具有uniq_val值的变化计数common_id值： http://sqlfiddle.com/#!15/e2c87/1/0

select common_id, 
     max(case when rn = 1 then uniq_val else null end) as uniq_val_1, 
     max(case when rn = 2 then uniq_val else null end) as uniq_val_2, 
     max(case when rn = 3 then uniq_val else null end) as uniq_val_3, 
     max(case when rn = 4 then uniq_val else null end) as uniq_val_4, 
     max(case when rn = 5 then uniq_val else null end) as uniq_val_5, 
     max(case when rn = 6 then uniq_val else null end) as uniq_val_6, 
     max(case when rn = 7 then uniq_val else null end) as uniq_val_7, 
     max(case when rn = 8 then uniq_val else null end) as uniq_val_8, 
     max(case when rn = 9 then uniq_val else null end) as uniq_val_9, 
     max(case when rn = 10 then uniq_val else null end) as uniq_val_10 
from(
select row_number() over (partition by common_id order by common_id, uniq_val) as rn, 
     common_id, 
     uniq_val 
    from my_table 
order by common_id, uniq_val) x 
group by common_id 
order by common_id