ALTER TABLE tablename MODIFY columnname varchar2(100)
ALTER TABLE Customers
MODIFY age VARCHAR(2);
ALTER TABLE products
ADD CONSTRAINT fk_supplier
FOREIGN KEY (supplier_id)
REFERENCES supplier(supplier_id);
ALTER TABLE table_name
ADD CONSTRAINT constraint_name
FOREIGN KEY (column1, column2, ... column_n)
REFERENCES parent_table (column1, column2, ... column_n);
ALTER TABLE table_name
ADD column_name data_type constraint;
Code language: SQL (Structured Query Language) (sql)