How can I add a Sequence to an existing table in a new field called the User_Id? I'm using Oracle SQL Developer version 3.0.04, and it provides an option to create a sequence, which I did, called Log_Seq. So I need to put this sequence in the table Final_Log under a column named User_Id. I'm stuck at this part. I would appreciate any help I can get!
You don't "add" a sequence to an existing table at least in existing Oracle versions. A database sequence is an database object that application code must manage with specific SQL data manipulation language (DML) statements. You need to modify application code to add or modify SQL statements.
See example from Admin. Guide http://docs.oracle.com/cd/E11882_01/server.112/e25494/views002.htm#ADMIN11796 .