SQL Antipatterns, Volume 1

Solution: Create an Intersection Table

Instead of storing the account_id in the Products table, store it in a separate table, so each individual value of that attribute occupies a separate row. This new table Contacts implements a many-to-many relationship between Products and Accounts:

Jaywalking/soln/create.sql

​CREATE​ ​TABLE​ Contacts (
  product_id  ​BIGINT​ ​UNSIGNED​ ​NOT​ ​NULL​,
  account_id  ​BIGINT​ ​UNSIGNED​ ​NOT​ ​NULL​,
  ​PRIMARY​ ​KEY​ (product_id, account_id),
  ​FOREIGN​ ​KEY​ (product_id) ​REFERENCES​ Products(product_id),
  ​FOREIGN​ ​KEY​ (account_id) ​REFERENCES​ Accounts(account_id)
);

​INSERT​ ​INTO​ Contacts ...