Foreign Key constraint in Derby

Question

Ok first off i have looked at google for hours trying to make my foreign key constraint work and no luck so far.

I will post the variations i have tried (which is basically every one i have seen on google).

This is my create statement which works perfectly, now i try to add a foreign key on Username column.

public final String CREATE_QUESTIONS_TABLE = "CREATE TABLE Questions(QuestionID INTEGER PRIMARY KEY GENERATED ALWAYS AS IDENTITY,"
        + "SubmittedTime TIMESTAMP NOT NULL,"
        + "Title VARCHAR(50) NOT NULL,"
        + "Text VARCHAR(300) NOT NULL,"
        + "Username VARCHAR(10),"
        + "Rating INTEGER DEFAULT 0 NOT NULL)";

I have tried adding these next to Username:

+ "Username VARCHAR(10) CONSTRAINT username_fk FOREIGN KEY (Username) REFERENCES Users(Username),"

+ "Username VARCHAR(10) CONSTRAINT username_fk REFERENCES Users(Username),"

And a couple others which I can't remember now (I had lots of tabs open)

I know it doesn't work since when i add these i get the following when i try SELECT from it

Schema 'USERNAME' does not exist

Which means it didn't create the table and i was trying to SELECT from a table that doesn't exist.

Please help me by telling what i need to write in order to define a column as a foreign key of another table.

I am trying to set Username of table Questions a foreign key of Username (Primary Key) of table Users.

This is with Derby and Java.

Answer 1

The Users table needs to be created first, followed by the Questions table.

The foreign key constraint is added at the end:

CREATE TABLE Questions
(
    QuestionID INTEGER PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
    SubmittedTime TIMESTAMP NOT NULL,
    Title VARCHAR(50) NOT NULL,
    Text VARCHAR(300) NOT NULL,
    Username VARCHAR(10),
    Rating INTEGER DEFAULT 0 NOT NULL,
    CONSTRAINT username_fk FOREIGN KEY (Username) REFERENCES Users(Username)
)