Question

I’m working on a project where the database has a few tables that contain a type_id field that stores id’s from multiple tables

for instance:

id | table_type | table id
==============================
1    ADDRESS      1
2    ADDRESS      2
3    CITY         1
4    CITY         2
4    ADDRESS      3
5    COUNTRY      1

the table_id field holds either an id from the Addresses table, or the Cities table, or the Countries table

I’m just wondering if this is good design. or should i avoid this whenever possible?

This table is used to grab all locations that a user has entered.

Answer 1

The answer is:

It Depends.

If the example table you gave was named Location and you’re using it to achieve type inheritance, where Address, City, and Country are specific types of Location, then this design can work. In this case, your primary key will be in the Location table, and each of the other tables will have a foreign key to Location. If that’s not how you’re using it, then this is not a properly normalized database design.