MySQL dynamic-pivot

Question

I have a table of product parts like this:

Parts

part_id      part_type      product_id
--------------------------------------
1            A              1
2            B              1
3            A              2
4            B              2
5            A              3
6            B              3

and I want a query that will return a table like this:

product_id      part_A_id      part_B_id
----------------------------------------
1               1              2
2               3              4
3               5              6

In its actual implementation there will be millions of product parts

What you're looking for is usually referred to as a dynamic pivot. — Joe Stefanelli, Sep 27 '12 at 21:15
@ruakh nothing pretty or useful, I've forgotten so much mysql — Vaughan, Sep 27 '12 at 21:19
Re: "nothing pretty or useful": Part of the point of showing what you've tried is simply to show that you've tried *something*. (A lot of question-askers don't, and it can be hard to summon the motivation to help those folks!) Another part is to help clarify the question; if you post a query that you've already written, and explain why it doesn't do what you need -- even if it doesn't come close -- then that can help clarify what it is that you do need. — ruakh, Sep 27 '12 at 21:28
@ruakh I hear what you are saying. In this case I thought my attempt would do little but muddy the waters. — Vaughan, Sep 27 '12 at 21:50
possible duplicate of [MySQL pivot row into dynamic number of columns](http://stackoverflow.com/questions/12004603/mysql-pivot-row-into-dynamic-number-of-columns) — RichardTheKiwi, May 03 '13 at 08:54
possible duplicate of [MySQL pivot table](http://stackoverflow.com/questions/7674786/mysql-pivot-table) — , Aug 15 '14 at 07:39

score 13 · Accepted Answer · answered Sep 27 '12 at 21:30

Unfortunately, MySQL does not have a PIVOT function but you can model it using an aggregate function and a CASE statement. For a dynamic version, you will need to use prepared statements:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'max(case when part_type = ''',
      part_type,
      ''' then part_id end) AS part_',
      part_type, '_id'
    )
  ) INTO @sql
FROM
  parts;
SET @sql = CONCAT('SELECT product_id, ', @sql, ' 
                  FROM parts 
                   GROUP BY product_id');

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

See SQL Fiddle With Demo

If you had only a few columns, then you can use a Static version:

select product_id,
  max(case when part_type ='A' then part_id end) as Part_A_Id,
  max(case when part_type ='B' then part_id end) as Part_B_Id
from parts
group by product_id

Why is max here ? Is it because it needs to be aggreate function there and it also could be sum or something else ? — Harlsten, Jan 29 '16 at 18:23
@Harlsten There has to be an aggregate function for this. `sum` wouldn't make sense because it's a `part_id`, for this particular example you'd need to use `max` or `min`. — Taryn, Jan 29 '16 at 18:28

score 1 · Answer 2 · edited May 23 '17 at 12:22

1

SQL Server has a PIVOT keyword, but with MySQL you will need to use either a lot of CASE/IF statements or a lot of JOINs.

Here is a previous post of how to do this.

edited May 23 '17 at 12:22

Community

1
1

answered Sep 27 '12 at 21:31

PeteGO

5,597
3
39
70

score -3 · Answer 3 · answered Sep 27 '12 at 21:27

-3

just reference it twice - (you don't really have much of a question here)

select a.product_id, a.part_id "part_a_id", b.part_id "part_b_id"
from parts a, parts b
where a.product_id = b.product_id

answered Sep 27 '12 at 21:27

Randy

16,480
1
37
55

I think you misread the question. You should go back and re-examine his example. – ajon Sep 27 '12 at 21:55
i think this produces the results requested. the question is poor imo. – Randy Sep 28 '12 at 01:16
Unless I am mistaken this produces additional results that are not in his results. For example: it would produce a row with (1,1,1) as well as (1,1,2) as well as (1,2,1) as well as (1,2,2). – ajon Sep 28 '12 at 05:44

MySQL dynamic-pivot

3 Answers3

Linked

Related