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POadd column to mysql table if it does not exist
 

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    <p>My research and experiments haven't yielded an answer yet, so I am hoping for some help.</p> <p>I am modifying the install file of an application which in previous versions did not have a column which I want to add now. I do not want to add the column manually, but in the installation file and only if the new column does not already exist in the table.</p> <p>The table is created as follows:</p> <pre><code>CREATE TABLE IF NOT EXISTS `#__comm_subscribers` ( `subscriber_id` int(11) NOT NULL auto_increment, `user_id` int(11) NOT NULL default '0', `subscriber_name` varchar(64) NOT NULL default '', `subscriber_surname` varchar(64) NOT NULL default '', `subscriber_email` varchar(64) NOT NULL default '', `confirmed` tinyint(1) NOT NULL default '0', `subscribe_date` datetime NOT NULL default '0000-00-00 00:00:00', PRIMARY KEY (`subscriber_id`), UNIQUE KEY `subscriber_email` (`subscriber_email`) ) ENGINE=MyISAM CHARACTER SET 'utf8' COLLATE 'utf8_general_ci' COMMENT='Subscribers for Comm are stored here.'; </code></pre> <p>If I add the following, below the create table statement, then I am not sure what happens if the column already exists (and perhaps is populated):</p> <pre><code>ALTER TABLE `#__comm_subscribers` ADD `subscriber_surname`; ALTER TABLE `#__comm_subscribers` MODIFY `subscriber_surname` varchar(64) NOT NULL default ''; </code></pre> <p>So, I tried the following which I found somewhere. This does not seem to work but I am not entirely sure I used it properly.</p> <pre><code>/*delimiter '//' CREATE PROCEDURE addcol() BEGIN IF NOT EXISTS( SELECT * FROM information_schema.COLUMNS WHERE COLUMN_NAME='subscriber_surname' AND TABLE_NAME='#__comm_subscribers' ) THEN ALTER TABLE `#__comm_subscribers` ADD COLUMN `subscriber_surname` varchar(64) NOT NULL default ''; END IF; END; // delimiter ';' CALL addcol(); DROP PROCEDURE addcol;*/ </code></pre> <p>Does anyone have a good way to do this?</p>
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    1. COAltering information_schema.COLUMNS, i.e. what the stored procedure does, is the way to go IMHO. What part of it "does not seem to work"?
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