将动态列转换为行

Question

我想知道如何将Table_1转换为Expected_Result_Table：

Table1
-----------------------------------------
Id       abc  brt ccc ddq eee fff gga hxx
-----------------------------------------
12345     0    1   0   5   0   2   0   0  
21321     0    0   0   0   0   0   0   0   
33333     2    0   0   0   0   0   0   0   
41414     0    0   0   0   5   0   0   1   
55001     0    0   0   0   0   0   0   2   
60000     0    0   0   0   0   0   0   0 
77777     9    0   3   0   0   0   0   0

Expected_Result_Table
---------------------
Id      Word   Qty>0
---------------------
12345    brt    1
12345    ddq    5
12345    fff    2
33333    abc    2
41414    eee    5
41414    hxx    1
55001    hxx    2
77777    abc    9
77777    ccc    3

那么，如何将Table_1中的列转置，得到Expected_Result_Table，只考虑值大于0的情况？

- Romualdo Alves

Answer 1

MySQL没有UNPIVOT函数，但是您可以使用UNION ALL将列转换为行。

基本语法如下：

select id, word, qty
from
(
  select id, 'abc' word, abc qty
  from yt
  where abc > 0
  union all
  select id, 'brt', brt
  from yt
  where brt > 0
) d
order by id;

在您的情况下，您需要解决动态列的问题。如果是这种情况，那么您将需要使用准备语句来生成动态SQL：

SET @sql = NULL;

SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'select id, ''',
      c.column_name,
      ''' as word, ',
      c.column_name,
      ' as qty 
      from yt 
      where ',
      c.column_name,
      ' > 0'
    ) SEPARATOR ' UNION ALL '
  ) INTO @sql
FROM information_schema.columns c
where c.table_name = 'yt'
  and c.column_name not in ('id')
order by c.ordinal_position;

SET @sql 
  = CONCAT('select id, word, qty
           from
           (', @sql, ') x  order by id');


PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

请参见带有演示的SQL Fiddle

- Taryn

Answer 2

您基本上是将数据从列转换为行，可以使用 UNION ALL。筛选器可以应用于未枢轴的子查询，也可以分别应用于各个部分。

select id, Word, Qty from
(
  select id, 'abc' Word, abc Qty from table1 
  union all
  select id, 'brt', brt from table1
  union all
  select id, 'ccc', ccc from table1
  union all
  select id, 'ddq', ddq from table1
  union all
  select id, 'eee', eee from table1
  union all
  select id, 'fff', fff from table1
  union all
  select id, 'gga', gga from table1
  union all
  select id, 'hxx', hxx from table1
) x
where Qty > 0
order by id;

- RichardTheKiwi

---

谢谢，理查德。我的表格具有动态和未知的列。 - Romualdo Alves