MySQL unique column string

Question

Currently I have this table in my database:

CREATE TABLE `twMCUserDB` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `mc_userName` text NOT NULL,
  `mc_userPass` text NOT NULL,
  `tw_userName` text NOT NULL,
  `tw_userPass` text NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;

I want the column mc_userName to be unique too (just like id), but mc_userName must be a string.

I tried to make it also a primary key, but that didn’t work.

When I add data to the table, do I first have to check whether the mc_userName already exists? Or is there any built-in function in MySQL that I can use (in the insert query, or somewhere else)?

Solution 1

just add UNIQUE

`mc_userName` text NOT NULL UNIQUE,

or

CREATE TABLE `twMCUserDB` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `mc_userName` text NOT NULL,
  `mc_userPass` text NOT NULL,
  `tw_userName` text NOT NULL,
  `tw_userPass` text NOT NULL,
  PRIMARY KEY (`id`),
  CONSTRAINT tb_uq UNIQUE (mc_userName)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;

Solution 2

Why don't you make 'mc_userName ' the Primary Key instead of id? You will have to change the data type of mc_userName to VARCHAR as described in this post: MySQL error: key specification without a key length. Alternatively, create a composite primary key containing id and username.

If you can't do this because of the design of the database then use the EXISTS keyword in a query. Have a look here for more information: http://dev.mysql.com/doc/refman/5.0/en/exists-and-not-exists-subqueries.html

Comments

[Mathlight]

I can't do that, because i get the error MySQL Error 1170: BLOB/TEXT Column Used in Key Specification Without a Key Length... And i will take an look at that link

[Mathlight]

sorry, i meant that first part... Making the mc_userName the primary key instead of the id.... i get the error i sayed above

[w0051977]

I have made a change to my answer. Can you change the data type of mc_userName to VARCHAR?

[w0051977]

This link may help you: stackoverflow.com/questions/1827063/…

[Mathlight]

I tried to change it to var char, making the id not primairy anymore, but only the mc_userName, but then i get this error: `ERROR 1167: The used storage engine can't index column 'mc_userName'

[Mathlight]

How can i add that UNIQUE to the colum than? i'm using Navicat as database editor, and phpmyadmin, but can't find something that can handle this...

[John Woo]

you can try to alter the table by running this DDL: ALTER TABLE twMCUserDB ADD UNIQUE tb_uq (mc_userName)

[Mathlight]

That returns this: [Err] 1170 - BLOB/TEXT column 'mc_userName' used in key specification without a key length

[John Woo]

try changing the databatype to varchar(100) since it is username

[w0051977]

Don't forget that changing from a Text datatype to a VARCHAR may cause data to be truncated e.g. 'Hello' would become 'Hell' with VARCHAR(4).

[John Woo]

or varchar(50) will suffice

[Mathlight]

I think exists is indeed the best option. I hoped that there was some kind of simple way to do, but this is fine to...

[Mathlight]

That did work, but are there difrnce betwwen text and varchar?

[John Woo]

VARCHAR you can set a limit for how many chars it will accept per record, text is (virtually) unlimited which you don't necessarily want)