SQL: "Reverse" 转置 table

Question

从下面看到很多关于转置的问题table...

scanid | region | volume
-------------------------
1          A      34.4
1          B      32.1
1          C      29.1
2          A      32.4
2          B      33.2
2          C      35.6

到这个table.

scanid | A_volume | B_volume | C_volume
----------------------------------------
1        34.4         32.1      29.1
2        32.4         33.2      35.6

但是，我需要做相反的事情，并且无法解决这个问题。有人可以帮忙吗？

谢谢。

Answer 1

您可以使用 UNION 子句非常简单地完成此操作：

Select Scan_ID, 'A' as Region, A_Volume as volume
    union all
Select Scan_ID, 'B' as Region, B_Volume as volume
    union all
Select Scan_ID, 'C' as Region, C_Volume as volume

Answer 2

不清楚你如何恢复 "A"、"B"、"C" 值，所以我只是添加它们

准备：

t=# create table s188 (scanid int,a float, b float,c float);
CREATE TABLE
t=# insert into s188 select 1,2,3,4;
INSERT 0 1
t=# insert into s188 select 2,12,13,14;
INSERT 0 1
t=# select * from s188;
 scanid | a  | b  | c
--------+----+----+----
      1 |  2 |  3 |  4
      2 | 12 | 13 | 14
(2 rows)

select:

t=# with a as (
  select scanid,unnest(array[a,b,c]) from s188
)
select scanid,chr((row_number() over (partition by scanid))::int + 64),unnest
from a;
 scanid | chr | unnest
--------+-----+--------
      1 | A   |      2
      1 | B   |      3
      1 | C   |      4
      2 | A   |     12
      2 | B   |     13
      2 | C   |     14
(6 rows)

以及来自 a_horse_with_no_name

的更简洁的解决方案

t=# with a as (
  select scanid, x.*
  from s188, unnest(array[a,b,c]) with ordinality as x(volume,idx)
)
select scanid,
       chr(idx::int + 64) as region,
       volume
from a;
 scanid | region | volume
--------+--------+--------
      1 | A      |      2
      1 | B      |      3
      1 | C      |      4
      2 | A      |     12
      2 | B      |     13
      2 | C      |     14
(6 rows)

SQL: "Reverse" 转置 table

SQL: "Reverse" transpose a table

sql

postgresql

unpivot