MySQL triggers fire depending on the activation time and the event for a total of six unique trigger combinations. does not exist because nothing is replacing the old value upon removal. data.įinally, when removing a row of data, the OLD. When updating a table row, both modifiers are available.

value does not exist for an insert statement because there is no information exists in its place beforehand. This is because a table is updated with new content. The availability of the modifiers depends on the trigger event you use: Trigger EventĬhecking or modifying a value when trying to insert data makes the NEW. Triggers allow access to values from the table for comparison purposes using NEW and OLD. Triggers are a particular type of stored procedure associated with a specific table. Knowledge of basic MySQL commands (refer to our downloadable MySQL commands cheat sheet)Ī trigger is a named MySQL object that activates when an event occurs in a table.MySQL user account with root privileges.A system running MySQL on a database server.

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