Using CREATE TRIGGER statement you can create a trigger. You have to put the trigger name after the trigger statement.
Let’s see an example of Create Trigger:
For example we have two tables i.e. users and userhistory.
users:
userID
firstName
lastName
userhistory:
userID
last_update
Read Also: INSERT … ON DUPLICATE KEY UPDATE
Now we will create a trigger before update users table:
DELIMITER $$ CREATE TRIGGER before_user_update BEFORE UPDATE ON users FOR EACH ROW BEGIN INSERT INTO userhistory SET last_update = NOW(), userID = OLD.userID; END$$ DELIMITER ;
Whenever user update their information userhistory table also get updated automatically.
Triggers could be defined on the table, schema, view or database with which the event is associated.
Triggers can be written for the following purposes:
- To prevent invalid transactions
- Security authorizations impose
- Like auditing
- Referential integrity enforce
- Event logging
- Information store on table access
- Synchronous replication of tables
- Generate derived column values automatically
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