How to add extra constraint to table?

Question

This my table:

customer_id
user_id
password
email
first_name
last_name

My primary key is customer_id which is generated by the system. How can I prevent a user form creating multiple accounts?

Should I put a constrain on another column?

What's user_id ? Add at least a UNIQUE CONSTRAINT on email ? — Raphaël Althaus, Sep 27 '16 at 14:30

score 1 · Accepted Answer · answered Sep 27 '16 at 14:30

Create a unique index or constraint on however you identify the user. I'm not sure which columns you have in mind, but this would be typical:

alter table mytable add constraint unq_table_email unique (email);

You can have more than one unique constraint on the table.

score 0 · Answer 2 · answered Sep 27 '16 at 14:34

Here you don't have a username field so u can do is that you can make email field as unique. What I do is that I make email id unique and whenever user tries to register i check whether email id is present. Because email id is unique no two person can have same email id.

How to add extra constraint to table?

2 Answers2