I have a table:
table votes (
id,
user,
email,
address,
primary key(id),
);
How can I make the columns user, email, address unique - i.e., ensure that there isn't any pair of rows that has identical values for all three columns?
To add a unique constraint, you need to use two components:
ALTER TABLE - to change the table schema and,
ADD UNIQUE - to add the unique constraint.
You then can define your new unique key with the format 'name'('column1', 'column2'...)
So for your particular issue, you could use this command:
ALTER TABLE `votes` ADD UNIQUE `unique_index`(`user`, `email`, `address`);
I have a MySQL table:
CREATE TABLE `content_html` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`id_box_elements` int(11) DEFAULT NULL,
`id_router` int(11) DEFAULT NULL,
`content` mediumtext COLLATE utf8_czech_ci NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `my_uniq_id` (`id_box_elements`,`id_router`)
);
and the UNIQUE KEY works just as expected, it allows multiple NULL rows of id_box_elements and id_router.
I am running MySQL 5.1.42, so probably there was some update on the issue discussed above. Fortunately it works and hopefully it will stay that way.
UNIQUE KEY my_uniq_id? Just UNIQUE is fine (on current MariaDB, anyway).
{null, null} is not a set of unique values.Multi column unique indexes do not work in MySQL if you have a NULL value in row as MySQL treats NULL as a unique value and at least currently has no logic to work around it in multi-column indexes. Yes the behavior is insane, because it limits a lot of legitimate applications of multi-column indexes, but it is what it is... As of yet, it is a bug that has been stamped with "will not fix" on the MySQL bug-track...
Have you tried this ?
UNIQUE KEY `thekey` (`user`,`email`,`address`)
UNIQUE KEY thekey` (user,email,address)`. I'm using MYSQL version 5.5.24 You can set this even in PHPMYADMIN if you are using it. I'm using the 3.5.1 version of PMA.This works for mysql version 5.5.32
ALTER TABLE `tablename` ADD UNIQUE (`column1` ,`column2`);
MySql 5 or higher behaves like this (I've just tested):
Example:
PRODUCT_NAME, PRODUCT_VERSION
'glass', null
'glass', null
'wine', 1
Now if you try to insert ('wine', 1) again it will report a constraint violation
You can add multiple-column unique indexes via phpMyAdmin. (I tested in version 4.0.4)
Navigate to the structure page for your target table. Add a unique index to one of the columns. Expand the Indexes list on the bottom of the structure page to see the unique index you just added. Click the edit icon, and in the following dialog you can add additional columns to that unique index.
this tutorial works for me
ALTER TABLE table_name
ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ... column_n);
I do it like this:
CREATE UNIQUE INDEX index_name ON TableName (Column1, Column2, Column3);
My convention for a unique index_name is TableName_Column1_Column2_Column3_uindex.
If You are creating table in mysql then use following :
create table package_template_mapping (
mapping_id int(10) not null auto_increment ,
template_id int(10) NOT NULL ,
package_id int(10) NOT NULL ,
remark varchar(100),
primary key (mapping_id) ,
UNIQUE KEY template_fun_id (template_id , package_id)
);
For adding unique index following are required:
1) table_name
2) index_name
3) columns on which you want to add index
ALTER TABLE `tablename`
ADD UNIQUE index-name
(`column1` ,`column2`,`column3`,...,`columnN`);
In your case we can create unique index as follows:
ALTER TABLE `votes`ADD
UNIQUE <votesuniqueindex>;(`user` ,`email`,`address`);
If you want to avoid duplicates in future. Create another column say id2.
UPDATE tablename SET id2 = id;
Now add the unique on two columns:
alter table tablename add unique index(columnname, id2);
First get rid of existing duplicates
delete a from votes as a, votes as b where a.id < b.id
and a.user <=> b.user and a.email <=> b.email
and a.address <=> b.address;
Then add the unique constraint
ALTER TABLE votes ADD UNIQUE unique_index(user, email, address);
Verify the constraint with
SHOW CREATE TABLE votes;
Note that user, email, address will be considered unique if any of them has null value in it.
For PostgreSQL... It didn't work for me with index; it gave me an error, so I did this:
alter table table_name
add unique(column_name_1,column_name_2);
PostgreSQL gave unique index its own name. I guess you can change the name of index in the options for the table, if it is needed to be changed...
In MySQL Workbench:
