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add a unique key to 'message_id' bigint() in an existing table

how to add a unique key to an existing table
`message_id` bigint(20) default NULL,

CREATE TABLE `a_messages2` (
`a_messages_id` int(11) NOT NULL auto_increment,
`conversation_id` bigint(20) default NULL,
`profile_id` varchar(20) default NULL,
`sender` varchar(20) default NULL,
`message_id` bigint(20) default NULL,
`message_text` varchar(1000) default NULL,
`dateAgo` varchar(20) default NULL,
`message_read` tinyint(4) default NULL,
`this_user` varchar(20) default NULL,
PRIMARY KEY (`a_messages_id`)
) ENGINE=MyISAM AUTO_INCREMENT=7054 DEFAULT CHARSET=utf8;

OmniUnlimited

"ALTER TABLE `a_messages2`ADD COLUMN `message_id` bigint(20) default NULL AFTER `a_messages_id`"
"ALTER TABLE `a_messages2`ADD UNIQUE KEY `mid` (message_id);"

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The key name "mid" can be any name you want.

rgb192

ASKER

I do not understand that
The key name "mid" can be any name you want.

OmniUnlimited

The key must be given a unique name. In the example I gave you, I called it "mid", but you can call it anything you like:

"ALTER TABLE `a_messages2`ADD UNIQUE KEY `PutTheNameOfTheKeyHere` (message_id);"

rgb192

ASKER

would there be any mysql select statements that call this unique 'putTheNameOfTheKeyHere' name

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OmniUnlimited

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rgb192

ASKER

thanks for the key information