如何转动？如何将多行转换为多列的一行？

I have two tables which I want to combine. The first table is with clients and the other with products. Currently I have 22 products, but I want to have a flexible DB design so instead of having 22 columns in the product DB, I have 1 row for each product for each client so if I add or remove 1 product overall, I don't have to change the DB structure. I have two tables which I want to combine. The