Updating a table with a single UPDATE statement vs several UPDATE statements CREATE TABLE `messages` (
  `mes_id` mediumint(8) unsigned NOT NULL AUTO_INCREMENT COMMENT 'номер объявления',
  `date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'дата/время дачи/изменения объявления',
  `expire` date NOT NULL COMMENT 'Дата истечения объявления',
  `paid_top_cat` tinyint(1) unsigned NOT NULL DEFAULT '0' COMMENT 'Наверху в разделе: 0 - нет, 1 - запрошен, 2 - включен',
  `paid_top_main` tinyint(1) unsigned NOT NULL DEFAULT '0' COMMENT 'Наверху на главной: 0 - нет, 1 - запрошен, 2 - включен',
  `paid_links` tinyint(1) unsigned NOT NULL DEFAULT '0' COMMENT 'Использование ссылок: 0 - нет, 1 - запрошен, 2 - включен',
  `paid_border` tinyint(1) unsigned NOT NULL DEFAULT '0' COMMENT 'Использование рамки: 0 - нет, 1 - запрошен, 2 - включен',
  `expire_top_cat` date DEFAULT NULL,
  `expire_top_main` date DEFAULT NULL,
  `expire_links` date DEFAULT NULL,
  `expire_border` date DEFAULT NULL,
  PRIMARY KEY (`mes_id`),
  # more fields
) ENGINE=MyISAM ;


I need to update some fields of a table dependently on some fields of the same table. Is the following in an UPDATE a good idea? paid_top_cat=IF(paid_top_cat=2 AND expire_to_cat&lt;NOW(), 1, paid_top_cat), expire_top_cat=IF(expire_top_cat&lt;NOW(), NULL, expire_top_cat) and so on for other expire_* and paid_* fields in a single statement.

What are arguments pro and counter to use this tricky UPDATE statements with many IF functions vs updating every column (or rather a pair of paid_* and expire_* columns) at once, so running UPDATE max 4 times?

MySQL.
When update executed once it's guaranteed that all rows that satisfy conditions will be updated (or none in case of error). 4 separate updates may update different rows (something may change between updates, and you're using MyIsam, so transactions won't help;  in addition, your update depends on non-deterministic NOW()  ). 

Another point is that each UPDATE locks set of rows , so 4 updates will lock rows 4 times even if the same rows are affected(in case of MyISAM)