Sitecore link of future refernces

 Below are some links that are very useful for Sitecore implementations -

Add new fields to the catalog item template -

https://doc.sitecore.com/developers/93/sitecore-experience-commerce/en/add-new-fields-to-a-catalog-item-template.html

https://www.ipointsystems.com/blog/2013/may/adding-custom-fields-to-sitecore-user-part-1

Good article on sql server Foreign Key implementation 

https://www.mssqltips.com/sqlservertip/5919/sql-server-referential-integrity-across-databases-using-triggers/