Example That Uses the Single-Column Constraint Format

The following example uses the single-column constraint format to create a referential relationship between the sub_accounts and accounts tables. The ref_num column in the sub_accounts table references the acc_num column (the primary key) in the accounts table.

CREATE TABLE accounts (
   acc_num INTEGER PRIMARY KEY,
   acc_type INTEGER,
   acc_descr CHAR(20))
CREATE TABLE sub_accounts (
   sub_acc INTEGER PRIMARY KEY,
   ref_num INTEGER REFERENCES accounts (acc_num),
   sub_descr CHAR(20))

When you use the single-column constraint format, you do not explicitly specify the ref_num column as a foreign key. To use the FOREIGN KEY keyword, use the Multiple-Column Constraint Format.