问题
I am using Oracle SQL Developer (the table modeling part) and I have found a symbol that I can't seem to be able to find an explanation for anywhere online:
I have been searching for a while now, and I'm at a total loss. I'm not sure what caused it in the first place, but I was hoping someone here might have seen it before and have an explanation.
回答1:
You tricked me, or I would have answered this much sooner. That's not an 'ER' symbol. ER = Entity Relation.
That symbol is from the relational diagram, which deals with tables and foreign keys vs entities and relations.
From the docs: Delete Rule: Action to take automatically when a row in the referenced table (in PK/UK Index) is deleted and rows with that value exist in the table containing this foreign key: NO ACTION (shown by a crossing line in diagrams) performs no action on these rows; CASCADE (shown by an "X") deletes these rows; SET NULL (shown by a small circle) sets null all columns in those rows that can be set to a null value; RESTRICT (also shown by one crossing line) prevents those rows from being deleted.
来源：https://stackoverflow.com/questions/36746239/found-an-unknown-relational-diagram-symbol-in-oracle-sql-developer