mysql pivot query results with GROUP BY

Question

I have a table to data that I want to export to a CSV. Ideally, I\'d like to switch the rows and columns around, so that the data is grouped a little better.

To expl

Answer 1

PIVOTing is neither easy (nor nice) to do. I prefer using CASE:

SELECT d.data_timestamp
     , SUM( CASE WHEN data_id =  1 THEN data_value ELSE 0 END ) AS 'input_1'
     , SUM( CASE WHEN data_id =  2 THEN data_value ELSE 0 END ) AS 'input_2'
     ...
     , SUM( CASE WHEN data_id = 20 THEN data_value ELSE 0 END ) AS 'input_20'
FROM data 
GROUP BY data_timestamp
ORDER BY data_timestamp ASC

but IF works in MySQL as well:

SELECT d.data_timestamp
     , SUM( IF(data_id =  1, data_value, 0) ) AS 'input_1'
     , SUM( IF(data_id =  2, data_value, 0) ) AS 'input_2'
     ...
     , SUM( IF(data_id = 20, data_value, 0) ) AS 'input_20'
FROM data 
GROUP BY data_timestamp
ORDER BY data_timestamp ASC

Alternatively, you can use a 20-level JOIN:

SELECT d.data_timestamp
     , d01.data_value AS 'input_1'
     , d02.data_value AS 'input_2'
     ...
     , d20.data_value AS 'input_20'
FROM
  ( SELECT DISTINCT d.data_timestamp
    FROM data
  ) AS d 
  LEFT JOIN data AS d01
    ON d01.data_timestamp = d.data_timestamp
    AND d01.data_id =  1
  LEFT JOIN data AS d02
    ON d02.data_timestamp = d.data_timestamp
    AND d02.data_id =  2
  ...                                   --- 20 JOINs
  LEFT JOIN data AS d20
    ON d20.data_timestamp = d.data_timestamp
    AND d20.data_id = 20
ORDER BY d.data_timestamp ASC

Answer 2

Just join the table to itself!

SELECT dt1.data_timestamp, dt1.input_1, dt2.input_2
FROM data_timestamp dt1
JOIN data_timestamp dt2 
    on dt1.data_timestamp = dt2.data_timestamp 
    and dt2.input_1 is null
WHERE dt1.input_2 is null;

Note that this query assumes input_2's value are present for every input_1 value. If that's not that case, use LEFT JOIN or CROSS JOIN etc