将动态列转置为行

Question

我想知道如何将Table_1 转为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，如何转置Table_1 中的列导致Expected_Result_Table，只考虑> 0 的值？

Answer 1

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

基本语法是：

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，您声明您需要动态列的解决方案。如果是这种情况，那么您将需要使用准备好的语句来生成动态 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;

见SQL Fiddle with Demo

Answer 2

您基本上是将数据从列转为行，您可以使用 UNION ALL。过滤器可以应用于非透视子查询，也可以单独应用于各个部分。

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;