MySQL pivot table in 1 to n relationship

Question

I have data like this table master_item

+-------+---------+
|item_id|item_name|
+-------+---------+
|  001  |  Car A  |
|  002  |  Car B  |
+-------+---------+

and relation into table process

+-------+--------+
|proc_id|proc_seq|
+-------+--------+
|  001  |   1    |
|  001  |   2    |
|  001  |   3    |
|  001  |   4    |
|  001  |   5    |
|  002  |   1    |
|  002  |   2    |
|  002  |   3    |
+-------+--------+

and i want result like this when i select item_id = 001

+-------+---------+-----+-----+-----+-----+-----+-----+-----+
|item_id|item_name|proc1|proc2|proc3|proc4|proc5|proc6|proc7|
+-------+---------+-----+-----+-----+-----+-----+-----+-----+
|  001  |  Car A  |  1  |  2  |  3  |  4  |  5  |     |     |
+-------+---------+-----+-----+-----+-----+-----+-----+-----+

what is the query to produce this result ?

Adopt simple query instead of doing this by pivot table query. And do the rest of the work in application level — 1000111

1000111 1000111 · Accepted Answer · 2016-08-15T08:42:22

The problem lies in PIVOT TABLE category.

Here you can accomplish your result through the query given below:

SET @sql := '';
SELECT 
CONCAT('SELECT 
MI.item_id,
MI.item_name,',
GROUP_CONCAT('MAX(CASE WHEN P.proc_seq =', P.proc_seq ,' THEN P.proc_seq END) AS ', 'proc',P.proc_seq,' '),
'FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id
WHERE MI.item_id = 1
GROUP BY P.proc_id') INTO @sql
FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id
WHERE item_id = 1
GROUP BY P.proc_id;


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

WORKING DEMO

But like I said, better do this kind of job in application logic. Otherwise it will be too cumbersome to make it done through MySQL alone.

EDIT:

In order to get result for each item_id

SET @sql := '';
SELECT 
CONCAT('SELECT 
MI.item_id,
MI.item_name,',
GROUP_CONCAT('MAX(CASE WHEN P.proc_seq =', P.proc_seq ,' THEN P.proc_seq END) AS ', 'proc',P.proc_seq,' '),
'FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id
GROUP BY P.proc_id') INTO @sql
FROM master_item MI
INNER JOIN process P ON MI.item_id = P.proc_id

WHERE
    item_id = (
        SELECT
            maxProcId.proc_id
        FROM
            (
                SELECT
                    proc_id,
                    COUNT(proc_seq) total
                FROM process
                GROUP BY proc_id
                ORDER BY total DESC
                LIMIT 1
            ) AS maxProcId
    )
GROUP BY
    P.proc_id;


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

Demonstrated here

MySQL pivot table in 1 to n relationship

2 Answers