Mysql – How to use Unique key via combinations of table fields

insertMySQLunique-constraintuniqueidentifier

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?

Best Answer

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`)
);

Related Solutions

Mysql – Unique combination key MySQL

Here is before trigger you can use to guarantee that id1 and id2 are inserted in min/max order

DELIMITER $$
CREATE TRIGGER mytable_bi BEFORE INSERT ON mytable
FOR EACH ROW
BEGIN
    DECLARE sum INT;
    SET sum = NEW.id1 + NEW.id2;
    SET NEW.id1 = (NEW.id1 + NEW.id2 - ABS(NEW.id1 - NEW.id2)) / 2;
    SET NEW.id2 = sum - NEW.id1;
END $$
DELIMITER ;

Here is some Sample Data:

DROP DATABASE IF EXISTS ryanzec;
CREATE DATABASE ryanzec;
USE ryanzec
CREATE TABLE mytable
(
    id1 INT NOT NULL,
    id2 INT NOT NULL,
    mapTypeId INT NOT NULL,
    primary key (id1,id2)
);
DELIMITER $$
CREATE TRIGGER mytable_bi BEFORE INSERT ON mytable
FOR EACH ROW
BEGIN
    DECLARE sum INT;
    SET sum = NEW.id1 + NEW.id2;
    SET NEW.id1 = (NEW.id1 + NEW.id2 - ABS(NEW.id1 - NEW.id2)) / 2;
    SET NEW.id2 = sum - NEW.id1;
END $$
DELIMITER ;
INSERT INTO mytable VALUES (1,2,3);
INSERT INTO mytable VALUES (2,1,3);
INSERT INTO mytable VALUES (5,4,6);
INSERT INTO mytable VALUES (4,5,6);
SELECT * FROM mytable;

Here it is the Sample Data Loaded

mysql> DROP DATABASE IF EXISTS ryanzec;
Query OK, 1 row affected (0.03 sec)

mysql> CREATE DATABASE ryanzec;
Query OK, 1 row affected (0.00 sec)

mysql> USE ryanzec
Database changed
mysql> CREATE TABLE mytable
    -> (
    ->     id1 INT NOT NULL,
    ->     id2 INT NOT NULL,
    ->     mapTypeId INT NOT NULL,
    ->     primary key (id1,id2)
    -> );
Query OK, 0 rows affected (0.10 sec)

mysql> DELIMITER $$
mysql> CREATE TRIGGER mytable_bi BEFORE INSERT ON mytable
    -> FOR EACH ROW
    -> BEGIN
    ->     DECLARE sum INT;
    ->     SET sum = NEW.id1 + NEW.id2;
    ->     SET NEW.id1 = (NEW.id1 + NEW.id2 - ABS(NEW.id1 - NEW.id2)) / 2;
    ->     SET NEW.id2 = sum - NEW.id1;
    -> END $$
Query OK, 0 rows affected (0.10 sec)

mysql> DELIMITER ;

Watch What Happens When I Insert the Rows:

mysql> INSERT INTO mytable VALUES (1,2,3);
Query OK, 1 row affected (0.06 sec)

mysql> INSERT INTO mytable VALUES (2,1,3);
ERROR 1062 (23000): Duplicate entry '1-2' for key 'PRIMARY'
mysql> INSERT INTO mytable VALUES (5,4,6);
Query OK, 1 row affected (0.07 sec)

mysql> INSERT INTO mytable VALUES (4,5,6);
ERROR 1062 (23000): Duplicate entry '4-5' for key 'PRIMARY'
mysql> SELECT * FROM mytable;
+-----+-----+-----------+
| id1 | id2 | mapTypeId |
+-----+-----+-----------+
|   1 |   2 |         3 |
|   4 |   5 |         6 |
+-----+-----+-----------+
2 rows in set (0.00 sec)

mysql>

Now, no matter what order id1 and id2 are entered, id1 will always be less than or equal to id2

This may not be contextually what you want because id1 and id2 are unique identifiers.

Sql-server – UNIQUE index key violation

There is a lot to grasp if you want to fully understand all of the intricacies of locking and isolation levels in SQL Server, and your question is essentially leading you in this direction.

All of the information is available at http://msdn.microsoft.com/en-us/library/ms173763.aspx, although it's not an easy read. An easier read is available at http://databases.about.com/od/sqlserver/a/isolationmodels.htm - pay particular attention to the "phantom reads" section.

For what you are trying to do you would need BOTH transactions running with an isolation level of "SERIALIZABLE". What this basically means is that they will run "as if" one was run after the other - that they were actually serialized.

What is happening is that BOTH the transactions decide that the same record needs to be inserted, and then BOTH try to insert that same record. The lock that is taken by the test logic is separate from the lock that is taken for the insert, which allows this to happen. SERIALIZABLE will stop this from happening with it's "Other transactions cannot insert new rows with key values that would fall in the range of keys read by any statements in the current transaction until the current transaction completes" clause. Another way to think of this is that the read locks from the test need to be held until the whole transaction completes. This can be specified using a HOLDLOCK query hint; but I have to say that I've not personally played with using HOLDLOCK, but just with the "SET TRANSACTION ISOLATION LEVEL SERIALIZABLE" version.

Best Answer

Related Solutions

Mysql – Unique combination key MySQL

Sql-server – UNIQUE index key violation

Related Question