I would like to create an after update trigger that runs only once even if mult开发者_运维百科iple rows have been updated.
Nope: http://dev.mysql.com/doc/refman/5.0/en/faqs-triggers.html#qandaitem-23-5-1-11
In MySQL 5.0, all triggers are FOR EACH ROW—that is, the trigger is activated for each row that is inserted, updated, or deleted.
However, see the following hack.
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