Why does the program complain about creating a foreign key?

Question

MySQL

Faced an inexplicable problem yet
. I create tables in DBForge, and faced such an error when creating foreign keys .

Moreover, I create keys in different ways




. I am studying and this needs to be done as part of a course project

Answer 1

Show definitions of other tables.
And there could be several reasons:

• parent tables/columns do not exist
  
• column types in child/parent are different
  
• parent column has no uniqueness constraint (KEY/UNIQUE)
  
• MyISAM engine (hehe)