MySQL pivot row into dynamic number of columns

Question

Lets say I have three different MySQL tables:

Table products:

id | name  1   Product A  2   Product B 

Table partners:

id | name  1   Partner A  2   Partner B 

Table sales:

partners_id | products_id           1             2           2             5           1             5           1             3           1             4           1             5           2             2           2             4           2             3           1             1 

I would like to get a table with partners in the rows and products as columns. So far I was able to get an output like this:

name      | name      | COUNT( * ) Partner A   Product A          1 Partner A   Product B          1 Partner A   Product C          1 Partner A   Product D          1 Partner A   Product E          2 Partner B   Product B          1 Partner B   Product C          1 Partner B   Product D          1 Partner B   Product E          1 

Using this query:

SELECT partners.name, products.name, COUNT( * )  FROM sales JOIN products ON sales.products_id = products.id JOIN partners ON sales.partners_id = partners.id GROUP BY sales.partners_id, sales.products_id LIMIT 0 , 30 

but I would like to have instead something like:

partner_name | Product A | Product B | Product C | Product D | Product E Partner A              1           1           1           1           2 Partner B              0           1           1           1           1 

The problem is that I cannot tell how many products I will have so the column number needs to change dynamically depending on the rows in the products table.

This very good answer does not seem to work with mysql: T-SQL Pivot? Possibility of creating table columns from row values

Answer 1

Unfortunately MySQL does not have a PIVOT function which is basically what you are trying to do. So you will need to use an aggregate function with a CASE statement:

select pt.partner_name,   count(case when pd.product_name = 'Product A' THEN 1 END) ProductA,   count(case when pd.product_name = 'Product B' THEN 1 END) ProductB,   count(case when pd.product_name = 'Product C' THEN 1 END) ProductC,   count(case when pd.product_name = 'Product D' THEN 1 END) ProductD,   count(case when pd.product_name = 'Product E' THEN 1 END) ProductE from partners pt left join sales s   on pt.part_id = s.partner_id left join products pd   on s.product_id = pd.prod_id group by pt.partner_name 

See SQL Demo

Since you do not know the Products you will probably want to perform this dynamically. This can be done using prepared statements.

With dynamic pivot tables (transform rows to columns) your code would look like this:

SET @sql = NULL; SELECT   GROUP_CONCAT(DISTINCT     CONCAT(       'count(case when Product_Name = ''',       Product_Name,       ''' then 1 end) AS ',       replace(Product_Name, ' ', '')     )   ) INTO @sql from products;  SET @sql = CONCAT('SELECT pt.partner_name, ', @sql, ' from partners pt left join sales s   on pt.part_id = s.partner_id left join products pd   on s.product_id = pd.prod_id group by pt.partner_name');  PREPARE stmt FROM @sql; EXECUTE stmt; DEALLOCATE PREPARE stmt; 

See SQL Demo

It's probably worth noting that GROUP_CONCAT is by default limited to 1024 bytes. You can work around this by setting it higher for the duration of your procedure, ie. SET @@group_concat_max_len = 32000;