删除一行中的重复（2 列的组合）值

Question

我需要删除连续出现的重复值。 喜欢：

C1 | C2 | C3 | C4 | C5 | C6
----------------------------
1  | 2  |  1 | 2  | 1  | 3
1  | 2  |  1 | 3  | 1  | 4
1  |NULL|  1 |NULL| 1  |NULL

查询的输出应该是：

C1 | C2 | C3 | C4 | C5 | C6
----------------------------
1  | 2  |  1 | 3  |NULL|NULL
1  | 2  |  1 | 3  | 1  | 4
1  |NULL|NULL|NULL|NULL|NULL

如您所见，两列的组合在一行中应该是唯一的。

在第 1 行：
1/2 的组合是重复的，因此将其删除并且 1/3 在 c5/c6 中被移动到 c3/c4

在第 2 行：
1/2 , 1/3, 1/4 的组合没有重复，所以结果没有变化

在第 3 行：
所有 3 种组合都相同，因为所有组合中都存在 1/NULL，因此 c3 到 c6 设置为 null。

提前致谢

Answer 1

也许有一个更聪明的方法......但你可以将它们转换成对，不同的（在这种情况下是联合），然后转回。

with pairs as (
    select id, c1 as x, c2 as y from mytable
    union
    select id, c3, c4 from mytable
    union 
    select id, c5, c6 from mytable
)
select id, 
       max(decode(rn,1,x)) c1,
       max(decode(rn,1,y)) c2,
       max(decode(rn,2,x)) c3,
       max(decode(rn,2,y)) c4,
       max(decode(rn,3,x)) c5,
       max(decode(rn,3,y)) c6
from (
    select id, x, y, row_number() over (partition by id) rn
    from pairs
) as foo
group by id

Answer 2

这个可行 - 包含用于测试的数据，但可能需要一些时间才能理解

提示：取消注释 --debug 行下的代码 sn-ps，复制脚本直到只有这些代码 sn-ps 并将这部分粘贴到 SQL 提示符中以测试中间结果。

原理是获取行标识符来“记住”行；然后垂直旋转 - 不是 3 列到 1 列，而是 6 列到 3 对列；然后，使用 DISTINCT 进行重复数据删除；然后在去重中间行的行标识符中获取索引；然后使用该索引再次水平旋转。

像这样：

WITH
input(c1,c2,c3,c4,c5,c6) AS (
          SELECT 1,        2,1,        2,1,        3
UNION ALL SELECT 1,        2,1,        3,1,        4
UNION ALL SELECT 1,NULL::INT,1,NULL::INT,1,NULL::INT
)
,
-- need rowid
input_with_rowid AS (
SELECT ROW_NUMBER() OVER() AS rowid, * FROM input
)
,
-- three groupy of 2 columns, so pivot using 3 indexes
idx3(idx) AS (SELECT 1 UNION SELECT 2 UNION SELECT 3)
,
-- pivot vertically, two columns at a time and de-dupe
pivot_pair AS (
SELECT DISTINCT
  rowid
, CASE idx 
    WHEN 1 THEN c1
    WHEN 2 THEN c3
    WHEN 3 THEN c5
  END AS c1
, 
  CASE idx 
    WHEN 1 THEN c2
    WHEN 2 THEN c4
    WHEN 3 THEN c6
  END AS c2
FROM input_with_rowid CROSS JOIN idx3
)
-- debug
-- SELECT * FROM pivot_pair ORDER BY rowid;
,
-- add sequence per rowid
pivot_pair_with_seq AS (
SELECT
  rowid
, ROW_NUMBER() OVER(PARTITION BY rowid) AS seq
, c1
, c2
FROM pivot_pair
)
-- debug
-- SELECT * FROM pivot_pair_with_seq;

SELECT
  rowid
, MAX(CASE seq WHEN 1 THEN c1 END) AS c1
, MAX(CASE seq WHEN 1 THEN c2 END) AS c2
, MAX(CASE seq WHEN 2 THEN c1 END) AS c3
, MAX(CASE seq WHEN 2 THEN c2 END) AS c4
, MAX(CASE seq WHEN 3 THEN c1 END) AS c5
, MAX(CASE seq WHEN 3 THEN c2 END) AS c6
FROM pivot_pair_with_seq
GROUP BY rowid
ORDER BY rowid
;

rowid|c1|c2|c3|c4|c5|c6
    1| 1| 2| 1| 3|- |-
    2| 1| 2| 1| 3| 1| 4
    3| 1|- |- |- |- |-

Answer 3

将 marcothesane 的想法与枢轴/非枢轴运算符结合使用。如果应该对更多输入列进行重复数据删除，则更易于维护。这保持了源数据（列对）的顺序——而 marcothesane 的解决方案可能会根据输入数据重新排序列对。它也比marcothesane的慢一点。它仅适用于 11R1 及更高版本。

WITH
input(c1,c2,c3,c4,c5,c6) AS (
          SELECT 1,        2,1,        2,1,        3 from dual
UNION ALL SELECT 1,        2,1,        3,1,        4 from dual
UNION ALL SELECT 1,NULL ,1,NULL ,1,NULL   from dual
)
,
-- need rowid
input_with_rowid AS (
SELECT ROW_NUMBER() OVER (order by 1) AS row_id, input.* FROM input
),
unpivoted_pairs as
(
  select row_id, tuple_idx, val1, val2, row_number() over (partition by row_id, val1, val2 order by tuple_idx) as keep_first
  from input_with_rowid
  UnPivot include nulls(
          (val1, val2)  --measure 
                for tuple_idx in ((c1,c2) as 1,
                                  (c3,c4) as 2,
                                  (c5,c6) as 3)
          )
)
select row_id, 
       t1_val1 as c1,
       t1_val2 as c2,
       t2_val1 as c3,
       t2_val2 as c4,
       t3_val1 as c5,
       t3_val2 as c6
from (
      select row_id,  
             val1, val2, row_number() over (partition by row_id order by tuple_idx) as tuple_order
      from unpivoted_pairs
      where keep_first = 1
      )
pivot (sum(val1) as val1, sum(val2) as val2
       for tuple_order in ('1' as t1, '2' as t2, '3' as t3)
       )