Transposing Dynamic Columns to Rows

mysql, unpivot

Solution

MySQL does not have an UNPIVOT function, but you can convert your columns into rows using a `UNION ALL`.

The basic syntax is:

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;

In your case, you state that you need a solution for dynamic columns. If that is the case, then you will need to use a prepared statement to generate dynamic 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;

See SQL Fiddle with Demo

Problem

I'd like to know how to unpivot `Table_1` into `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 ``` So, How to transpose columns in `Table_1` resulting in `Expected_Result_Table`, considering only values > 0?

Original source