About Entity Relationship Diagram

Question

My question is about the inventory.Device table in this ERD (I can't attach image, please help refer it from https://dba.stackexchange.com/questions/25548/separate-archive-tables-or-soft-delete-for-inventory-database)

• Why there are lots of fields be named set as FK2, does it have some special meaning?
• The field isArchived is named as U5,U4,U1. What does it mean?

Many thanks

Answer 1

FK means foreign key. For practical purposes this is an indexed field that refers to the primary key of a table to make a relational link. There will generally be a referential integrity constraint associated with this index.

U means unique. This will be a unique index with matching constraint.

The numbers after FK and U are sequential numbers to indicate which constraint/index the column comprises, or is a part of. FK2 is the second foreign key, U1,U4,U5 are the first, fourth and fifth unique indexes. The order of these constraints is arbitrary. There is nothing special about being the first or second (etc) constraint.