移调动态列到行

Question

我想知道如何逆转置Table_1到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，如何转列Table_1导致Expected_Result_Table，只考虑值> 0 ？

Answer 1

MySQL没有一个UNPIVOT功能，但是您可以将列转换为使用UNION ALL行。

的基本语法是：

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; 

在你的情况，你的状态，你需要动态列的解决方案。如果是这样的话，那么你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

基本上，您可以将列中的数据转化为行，您可以使用UNION ALL。筛选器可以应用于未转义的子查询中，也可以单独应用于部件。

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;