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    <p>The problem is that the <code>IF</code> control flow construct only works in stored procedures (Just like all other <a href="http://dev.mysql.com/doc/refman/5.0/en/flow-control-constructs.html" rel="nofollow">Flow Control Constructs</a>... So you'd need to define a procedure to do what you're asking...</p> <p>So here's how to define sample procedure to do what you want:</p> <pre><code>DELIMITER // CREATE PROCEDURE myProcedure() BEGIN SET @cv = (SELECT `value` FROM `configs` WHERE `name` = 'cvDate'); IF @cv &lt;= STR_TO_DATE("2010/11/10 12:15:00") THEN ALTER TABLE `feeds` ADD `tone` VARCHAR( 255 ) NOT NULL AFTER `type` , ADD `authority` DECIMAL( 2, 1 ) NOT NULL DEFAULT '0.0' AFTER `tone`; END IF; UPDATE `configs` SET `value` = NOW() WHERE `name` = "cvDate"; END// DELIMITER ; </code></pre> <p>That will create it, then to run it, just do:</p> <pre><code>CALL myProcedure(); </code></pre> <p>See <a href="http://dev.mysql.com/doc/refman/5.0/en/create-procedure.html" rel="nofollow">the docs</a> for more info.</p> <p>You can actually even make it take parameters so you don't need to hard-code everything. But I'm not sure how you would do that based upon what you provided (I'm not sure what exactly you're trying to accomplish)...</p> <p>If you want to make it take a sql statement as a parameter (using <a href="http://dev.mysql.com/doc/refman/5.0/en/sql-syntax-prepared-statements.html" rel="nofollow">Prepared Statements</a> ):</p> <pre><code>DELIMITER // CREATE PROCEDURE myInputProcedure(IN updateDate DATETIME, IN sql TEXT) BEGIN SET @cv = (SELECT `value` FROM `configs` WHERE `name` = 'cvDate'); IF @cv &lt;= updateDate THEN PREPARE stmt1 FROM sql; EXECUTE stmt1; END IF; UPDATE `configs` SET `value` = NOW() WHERE `name` = "cvDate"; END// DELIMITER ; </code></pre> <p>Then, simply call it like this:</p> <pre><code>@sql = 'ALTER TABLE `feeds` ADD `tone` VARCHAR( 255 ) NOT NULL AFTER `type` , ADD `authority` DECIMAL( 2, 1 ) NOT NULL DEFAULT '0.0' AFTER `tone`;'; @date = STR_TO_DATE("2010/11/10 12:15:00"); CALL myInputProcedure(@date, @sql); </code></pre> <p>(Note that I added <code>@sql</code> and <code>@date</code> for readability, not because they are necessary)...</p>
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    1. COCare to explain the -1?
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    2. COI did the +1, not sure who did the minus -1. Could you give the OP a very simple example of a stored procedure?
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    3. CONice very helpful!
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