Foreign Key Problem (Base)
I am a complete beginner with databases, so there is probably a simple explanation, but I can't find it.
I am trying to build a database that will eventually generate tags for PLC and SCADA from the P&ID device list. I have ceated 3 tables, first for the P&ID devices, which uses the P&ID tag as the primary key (all unique) and has a column of device types (text)
The second table contains all the boolean tag suffixes, per device type, so device type is a primary key, same field details as in the P&ID table.
The third table is a repeat of the second, but for real tag suffixes (device type is a primary key)
I can create a 1:n relationship between the PID Tag table and the Boolean table but when I try to add a second 1:n between the PID Tags and the Real Tags I get this error (screenshot)
How do I resolve this? I can't find any way to add a foreign key (whatever that is) to a table?
Eventually I want to have tables for Integer tags as well