How to use Unique key via combinations of table fields?

Question

Take a look at the following sqlfiddle: http://sqlfiddle.com/#!2/dacb5/1

CREATE TABLE contacts 
    (
     id int auto_increment primary key, 
     name varchar(20), 
     network_id int,
     network_contact_id int
    );

INSERT INTO contacts
(name, network_id, network_contact_id)
VALUES
('John', 4, 10),
('Alex', 4, 11),
('Bob', 4, 12),
('Jeff', 4, 45),
('Bill', 7, 11),
('Walter', 7, 45),
('Jessie', 7, 360) ;

I have a basic table of contacts. The network_id and network_contact_id fields contain id numbers that link to other tables.

I want to be able to run INSERT IGNORE queries to this table, but I want to use the combination of the network_id and network_contact_id as the unique key to match against.

So for example, if I tried to insert a contact that had network_id = 4 and network_contact_id = 12, the INSERT IGNORE query would see that entry already exists, and ignore any error that was thrown.

So basically, network_id is not unique. network_contact_id is not unique. But the combination of the two is unique. How do I set this up? Would I have to have a single other field that is the concatenated values of the two other fields? Or is there a way to setup the keys for this table so it will do what I need?

score 9 · Accepted Answer · answered May 11 '12 at 21:12

9

Did you try

CREATE TABLE contacts (
 id int auto_increment primary key, 
 name varchar(20), 
 network_id int,
 network_contact_id int, 
 UNIQUE KEY (`network_id`, `network_contact_id`)
);

answered May 11 '12 at 21:12

Derek Downey

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score 6 · Answer 2 · edited May 23 '17 at 12:40

Change the table's definition by adding a UNIQUE KEY constraint on the combination of the two columns:

CREATE TABLE contacts 
    (
     id int auto_increment primary key, 
     name varchar(20), 
     network_id int,
     network_contact_id int,
     CONSTRAINT network_id_contact_id_UNIQUE
       UNIQUE KEY (network_id, network_contact_id)
    );

You should also check this answer by Bill Karwin on the differences between INSERT IGNORE, REPLACE and INSERT ... ON DUPLICATE KEY UPDATE

How to use Unique key via combinations of table fields?

2 Answers2