ALTER TABLE FOREIGN KEY从java到mysql

Question

Well, I want to make a modification in my database, so I need to use alter table but java seems to have problems making that.

This is the sentence

ALTER TABLE loans ADD FOREIGN KEY (id_reader) REFERENCES readers (id);

how do you execute it?

I was doing this:

rawStatement="ALTER TABLE loans ADD FOREIGN KEY (id_reader) REFERENCES readers (id);";
currentStatement = conn.createStatement();
currentStatement.execute(rawStatement); 

is the last line correct?

As far I know, execute must run everything.

Answer 1

Use this :

executeUpdate() 

instead of

execute()

Also if the constraint is already present it will throw an exception

Other things you should look out for:

• Does the user have the privileges to alter the table?

Answer 2

Try with the below code:

rawStatement="ALTER TABLE loans ADD FOREIGN KEY (id_reader) REFERENCES readers (id)"; 
PreparedStatement ps = conn.prepareStatement(rawStatement);
ps.executeUpdate();